snit(3)



snit(3tcl)              Snit's Not Incr Tcl, OO system              snit(3tcl)

______________________________________________________________________________

NAME
       snit - Snit's Not Incr Tcl

SYNOPSIS
       package require Tcl  8.5

       package require snit  ?2.3.2?

       snit::type name definition

       typevariable name ?-array? ?value?

       typemethod name arglist body

       typeconstructor body

       variable name ?-array? ?value?

       method name arglist body

       option namespec ?defaultValue?

       option namespec ?options...?

       constructor arglist body

       destructor body

       proc name args body

       delegate method name to comp ?as target?

       delegate method name ?to comp? using pattern

       delegate method * ?to comp? ?using pattern? ?except exceptions?

       delegate option namespec to comp

       delegate option namespec to comp as target

       delegate option * to comp

       delegate option * to comp except exceptions

       component comp ?-public method? ?-inherit flag?

       delegate typemethod name to comp ?as target?

       delegate typemethod name ?to comp? using pattern

       delegate typemethod * ?to comp? ?using pattern? ?except exceptions?

       typecomponent comp ?-public typemethod? ?-inherit flag?

       pragma ?options...?

       expose comp

       expose comp as method

       onconfigure name arglist body

       oncget name body

       snit::widget name definition

       widgetclass name

       hulltype type

       snit::widgetadaptor name definition

       snit::typemethod type name arglist body

       snit::method type name arglist body

       snit::macro name arglist body

       snit::compile which type body

       $type typemethod args...

       $type create name ?option value ...?

       $type info typevars ?pattern?

       $type info typemethods ?pattern?

       $type info args method

       $type info body method

       $type info default method aname varname

       $type info instances ?pattern?

       $type destroy

       $object method args...

       $object configure ?option? ?value? ...

       $object configurelist optionlist

       $object cget option

       $object destroy

       $object info type

       $object info vars ?pattern?

       $object info typevars ?pattern?

       $object info typemethods ?pattern?

       $object info options ?pattern?

       $object info methods ?pattern?

       $object info args method

       $object info body method

       $object info default method aname varname

       mymethod name ?args...?

       mytypemethod name ?args...?

       myproc name ?args...?

       myvar name

       mytypevar name

       from argvName option ?defvalue?

       install compName using objType objName args...

       installhull using widgetType args...

       installhull name

       variable name

       typevariable name

       varname name

       typevarname name

       codename name

       snit::boolean validate ?value?

       snit::boolean name

       snit::double validate ?value?

       snit::double name ?option value...?

       snit::enum validate ?value?

       snit::enum name ?option value...?

       snit::fpixels validate ?value?

       snit::fpixels name ?option value...?

       snit::integer validate ?value?

       snit::integer name ?option value...?

       snit::listtype validate ?value?

       snit::listtype name ?option value...?

       snit::pixels validate ?value?

       snit::pixels name ?option value...?

       snit::stringtype validate ?value?

       snit::stringtype name ?option value...?

       snit::window validate ?value?

       snit::window name

______________________________________________________________________________

DESCRIPTION
       Snit is a pure Tcl object and megawidget system.  It's unique among Tcl
       object systems in that it's based not on inheritance but on delegation.
       Object  systems  based  on  inheritance  only allow you to inherit from
       classes defined using the same system, which is limiting.  In  Tcl,  an
       object  is  anything  that acts like an object; it shouldn't matter how
       the object was implemented.  Snit is intended to help you build  appli-
       cations out of the materials at hand; thus, Snit is designed to be able
       to incorporate and build on any object, whether it's a  hand-coded  ob-
       ject,  a  Tk  widget,  an Incr Tcl object, a BWidget or almost anything
       else.

       This man page is intended to be a reference only; see the  accompanying
       snitfaq for a gentler, more tutorial introduction to Snit concepts.

SNIT VERSIONS
       This  man  page covers both Snit 2.2 and Snit 1.3.  The primary differ-
       ence between the two versions is simply that Snit  2.2  contains  speed
       optimizations  based  on new features of Tcl 8.5; Snit 1.3 supports all
       of Tcl 8.3, 8.4 and Tcl 8.5.  There are a  few  minor  inconsistencies;
       they  are  flagged in the body of the man page with the label "Snit 1.x
       Incompatibility"; they are also discussed in the snitfaq.

REFERENCE
   TYPE AND WIDGET DEFINITIONS
       Snit provides the following commands for defining new types:

       snit::type name definition
              Defines a new abstract data type called name.  If name is not  a
              fully  qualified command name, it is assumed to be a name in the
              namespace in which the snit::type command  was  called  (usually
              the  global  namespace).  It returns the fully qualified name of
              the new type.

              The type name is then a command that is used to  create  objects
              of the new type, along with other activities.

              The snit::type definition block is a script that may contain the
              following definitions:

              typevariable name ?-array? ?value?
                     Defines a type variable with the specified name, and  op-
                     tionally  the specified value.  Type variables are shared
                     by all instances of the type.  If the  -array  option  is
                     included,  then  value should be a dictionary; it will be
                     assigned to the variable using array set.

              typemethod name arglist body
                     Defines a type method, a subcommand of the new type  com-
                     mand,  with  the specified name, argument list, and body.
                     The arglist is a normal Tcl argument list and may contain
                     default  arguments and the args argument; however, it may
                     not contain the argument names  type,  self,  selfns,  or
                     win.

                     The variable type is automatically defined in the body to
                     the type's fully-qualified name.  In addition, type vari-
                     ables are automatically visible in the body of every type
                     method.

                     If the name consists of two or more tokens, Snit  handles
                     it specially:

                         typemethod {a b} {arg} { puts "Got $arg" }

                     This  statement implicitly defines a type method called a
                     which has a subcommand b.  b is called like this:

                         $type a b "Hello, world!"

                     a may have any number of subcommands.  This makes it pos-
                     sible  to  define  a  hierarchical command structure; see
                     method, below, for more examples.

                     Type methods can call  commands  from  the  namespace  in
                     which  the  type is defined without importing them, e.g.,
                     if the type name is ::parentns::typename, then the type's
                     type  methods can call ::parentns::someproc just as some-
                     proc.  Snit 1.x Incompatibility: This does  not  work  in
                     Snit  1.x, as it depends on namespace path, a new command
                     in Tcl 8.5.

                     Snit 1.x Incompatibility: In Snit 1.x, the following fol-
                     lowing two calls to this type method are equivalent:

                         $type a b "Hello, world!"
                         $type {a b} "Hello, world!"

                     In Snit 2.2, the second form is invalid.

              typeconstructor body
                     The  type  constructor's  body  is executed once when the
                     type is first defined; it is typically used to initialize
                     array-valued  type variables and to add entries to The Tk
                     Option Database.

                     The variable type is automatically defined in  the  body,
                     and  contains  the type's fully-qualified name.  In addi-
                     tion, type variables are  automatically  visible  in  the
                     body of the type constructor.

                     A type may define at most one type constructor.

                     The type constructor can call commands from the namespace
                     in which the type  is  defined  without  importing  them,
                     e.g.,  if the type name is ::parentns::typename, then the
                     type constructor can call  ::parentns::someproc  just  as
                     someproc.   Snit  1.x Incompatibility: This does not work
                     in Snit 1.x, as it depends on namespace path, a new  com-
                     mand in Tcl 8.5.

              variable name ?-array? ?value?
                     Defines  an instance variable, a private variable associ-
                     ated with each instance of this type, and optionally  its
                     initial  value.   If  the -array option is included, then
                     value should be a dictionary; it will be assigned to  the
                     variable using array set.

              method name arglist body
                     Defines an instance method, a subcommand of each instance
                     of this type, with the specified name, argument list  and
                     body.   The arglist is a normal Tcl argument list and may
                     contain default arguments and the args argument.

                     The method is implicitly passed the  following  arguments
                     as  well:  type,  which contains the fully-qualified type
                     name; self, which contains the current  instance  command
                     name;  selfns,  which contains the name of the instance's
                     private namespace; and win, which contains  the  original
                     instance name.  Consequently, the arglist may not contain
                     the argument names type, self, selfns, or win.

                     An instance method defined in this way is said to be  lo-
                     cally defined.

                     Type  and instance variables are automatically visible in
                     all instance methods.  If the type  has  locally  defined
                     options, the options array is also visible.

                     If  the name consists of two or more tokens, Snit handles
                     it specially:

                         method {a b} {} { ... }

                     This statement implicitly defines a method called a which
                     has a subcommand b.  b is called like this:

                         $self a b "Hello, world!"

                     a may have any number of subcommands.  This makes it pos-
                     sible to define a hierarchical command structure:

                     % snit::type dog {
                         method {tail wag}   {} {return "Wag, wag"}
                         method {tail droop} {} {return "Droop, droop"}
                     }
                     ::dog
                     % dog spot
                     ::spot
                     % spot tail wag
                     Wag, wag
                     % spot tail droop
                     Droop, droop
                     %

                     What we've done is implicitly  defined  a  "tail"  method
                     with  subcommands  "wag" and "droop".  Consequently, it's
                     an error to define "tail" explicitly.

                     Methods can call commands from the namespace in which the
                     type is defined without importing them, e.g., if the type
                     name is ::parentns::typename, then the type's methods can
                     call ::parentns::someproc just as someproc.  Snit 1.x In-
                     compatibility: This does not work in Snit 1.x, as it  de-
                     pends on namespace path, a new command in Tcl 8.5.

                     Snit 1.x Incompatibility: In Snit 1.x, the following fol-
                     lowing two calls to this method are equivalent:

                         $self a b "Hello, world!"
                         $self {a b} "Hello, world!"

                     In Snit 2.2, the second form is invalid.

              option namespec ?defaultValue?

              option namespec ?options...?
                     Defines an option for instances of this type, and option-
                     ally  gives  it  an initial value.  The initial value de-
                     faults to the empty string if no defaultValue  is  speci-
                     fied.

                     An  option  defined in this way is said to be locally de-
                     fined.

                     The namespec is a list defining the  option's  name,  re-
                     source name, and class name, e.g.:

                         option {-font font Font} {Courier 12}

                     The  option  name  must begin with a hyphen, and must not
                     contain any upper case letters.  The  resource  name  and
                     class  name  are optional; if not specified, the resource
                     name defaults to the option name, minus the  hyphen,  and
                     the  class  name  defaults  to the resource name with the
                     first letter capitalized.  Thus, the following  statement
                     is equivalent to the previous example:

                         option -font {Courier 12}

                     See The Tk Option Database for more information about re-
                     source and class names.

                     Options are normally set and retrieved using the standard
                     instance methods configure and cget; within instance code
                     (method  bodies,  etc.),  option  values  are   available
                     through the options array:

                         set myfont $options(-font)

                     If  the  type defines any option handlers (e.g., -config-
                     uremethod), then it should  probably  use  configure  and
                     cget to access its options to avoid subtle errors.

                     The option statement may include the following options:

                     -default defvalue
                            Defines  the  option's default value; the option's
                            default value will be "" otherwise.

                     -readonly flag
                            The flag can be any Boolean  value  recognized  by
                            Tcl.   If  flag  is true, then the option is read-
                            only--it can only be set using configure  or  con-
                            figurelist  at  creation time, i.e., in the type's
                            constructor.

                     -type type
                            Every locally-defined option may define its  vali-
                            dation  type,  which  may  be either the name of a
                            validation type or a specification for  a  valida-
                            tion subtype

                            For  example, an option may declare that its value
                            must be an integer by specifying snit::integer  as
                            its validation type:

                                option -number -type snit::integer

                            It  may  also declare that its value is an integer
                            between 1 and 10 by specifying a  validation  sub-
                            type:

                                option -number -type {snit::integer -min 1 -max 10}

                            If  a validation type or subtype is defined for an
                            option, then it will be used to validate  the  op-
                            tion's  value  whenever  it  is changed by the ob-
                            ject's configure or configurelist methods.  In ad-
                            dition,  all  such  options will have their values
                            validated automatically immediately after the con-
                            structor executes.

                            Snit defines a family of validation types and sub-
                            types, and it's quite simple to define  new  ones.
                            See  Validation  Types  for the complete list, and
                            Defining Validation Types for  an  explanation  of
                            how to define your own.

                     -cgetmethod methodName
                            Every  locally-defined  option may define a -cget-
                            method; it is called when the  option's  value  is
                            retrieved  using  the  cget  method.  Whatever the
                            method's body returns will be the return value  of
                            the call to cget.

                            The  named  method must take one argument, the op-
                            tion name.  For example, this code  is  equivalent
                            to (though slower than) Snit's default handling of
                            cget:

                                option -font -cgetmethod GetOption
                                method GetOption {option} {
                                    return $options($option)
                                }

                            Note that it's possible for any number of  options
                            to share a -cgetmethod.

                     -configuremethod methodName
                            Every locally-defined option may define a -config-
                            uremethod; it is called when the option's value is
                            set  using the configure or configurelist methods.
                            It is the named method's  responsibility  to  save
                            the option's value; in other words, the value will
                            not be saved to the  options()  array  unless  the
                            method saves it there.

                            The  named method must take two arguments, the op-
                            tion name and its new value.   For  example,  this
                            code  is equivalent to (though slower than) Snit's
                            default handling of configure:

                                option -font -configuremethod SetOption
                                method SetOption {option value} {
                                    set options($option) $value
                                }

                            Note that it's possible for any number of  options
                            to share a single -configuremethod.

                     -validatemethod methodName
                            Every  locally-defined  option may define a -vali-
                            datemethod; it is called when the  option's  value
                            is  set using the configure or configurelist meth-
                            ods, just before the  -configuremethod  (if  any).
                            It  is  the named method's responsibility to vali-
                            date the option's new value, and to throw an error
                            if the value is invalid.

                            The  named method must take two arguments, the op-
                            tion name and its new value.   For  example,  this
                            code  verifies that -flag's value is a valid Bool-
                            ean value:

                                option -font -validatemethod CheckBoolean
                                method CheckBoolean {option value} {
                                    if {![string is boolean -strict $value]} {
                                        error "option $option must have a boolean value."
                                    }
                                }

                            Note that it's possible for any number of  options
                            to share a single -validatemethod.

              constructor arglist body
                     The constructor definition specifies a body of code to be
                     executed when a new instance is created.  The arglist  is
                     a  normal Tcl argument list and may contain default argu-
                     ments and the args argument.

                     As with methods, the arguments type,  self,  selfns,  and
                     win  are  defined  implicitly,  and all type and instance
                     variables are automatically visible in its body.

                     If the definition doesn't explicitly define the construc-
                     tor,  Snit  defines one implicitly.  If the type declares
                     at least one option (whether locally or  by  delegation),
                     the default constructor will be defined as follows:

                         constructor {args} {
                             $self configurelist $args
                         }

                     For standard Tk widget behavior, the argument list should
                     be the single name args, as shown.

                     If the definition defines neither a constructor  nor  any
                     options, the default constructor is defined as follows:

                         constructor {} {}

                     As  with  methods, the constructor can call commands from
                     the namespace in which the type is  defined  without  im-
                     porting them, e.g., if the type name is ::parentns::type-
                     name, then the constructor can call  ::parentns::someproc
                     just  as  someproc.   Snit 1.x Incompatibility: This does
                     not work in Snit 1.x, as it depends on namespace path,  a
                     new command in Tcl 8.5.

              destructor body
                     The destructor is used to code any actions that must take
                     place when an instance of the type  is  destroyed:  typi-
                     cally,  the  destruction  of anything created in the con-
                     structor.

                     The destructor takes no explicit arguments; as with meth-
                     ods,  the  arguments type, self, selfns, and win, are de-
                     fined implicitly, and all type and instance variables are
                     automatically  visible in its body.  As with methods, the
                     destructor can call commands from the namespace in  which
                     the  type is defined without importing them, e.g., if the
                     type name is ::parentns::typename,  then  the  destructor
                     can call ::parentns::someproc just as someproc.  Snit 1.x
                     Incompatibility: This does not work in Snit  1.x,  as  it
                     depends on namespace path, a new command in Tcl 8.5.

              proc name args body
                     Defines a new Tcl procedure in the type's namespace.

                     The  defined  proc differs from a normal Tcl proc in that
                     all type variables are automatically visible.   The  proc
                     can  access  instance variables as well, provided that it
                     is passed selfns (with precisely that name) as one of its
                     arguments.

                     Although  they  are not implicitly defined for procs, the
                     argument names type, self, and win should be avoided.

                     As with methods and typemethods, procs can call  commands
                     from  the  namespace in which the type is defined without
                     importing  them,  e.g.,  if  the  type  name  is   ::par-
                     entns::typename, then the proc can call ::parentns::some-
                     proc just as someproc.  Snit  1.x  Incompatibility:  This
                     does  not  work  in  Snit 1.x, as it depends on namespace
                     path, a new command in Tcl 8.5.

              delegate method name to comp ?as target?
                     Delegates method name to component comp.  That  is,  when
                     method  name  is  called on an instance of this type, the
                     method and its arguments will be passed to the named com-
                     ponent's  command instead.  That is, the following state-
                     ment

                         delegate method wag to tail

                     is roughly equivalent to this explicitly defined method:

                         method wag {args} {
                             uplevel $tail wag $args
                         }

                     As with methods, the name may have  multiple  tokens;  in
                     this  case,  the  last token of the name is assumed to be
                     the name of the component's method.

                     The optional as clause allows you to  specify  the  dele-
                     gated method name and possibly add some arguments:

                         delegate method wagtail to tail as "wag briskly"

              A method cannot be both locally defined and delegated.

              Note: All forms of delegate method can delegate to both instance
              components and type components.

              delegate method name ?to comp? using pattern
                     In this form of the delegate statement, the using  clause
                     is  used  to  specify  the precise form of the command to
                     which method name name is delegated.  In this  form,  the
                     to clause is optional, since the chosen command might not
                     involve any particular component.

                     The value of the using clause is a list that may  contain
                     any  or  all  of  the following substitution codes; these
                     codes are substituted with the described value  to  build
                     the  delegated  command  prefix.  Note that the following
                     two statements are equivalent:

                         delegate method wag to tail
                         delegate method wag to tail using "%c %m"

                     Each element of the list becomes a single element of  the
                     delegated command--it is never reparsed as a string.

                     Substitutions:

                     %%     This is replaced with a single "%".  Thus, to pass
                            the string "%c" to the  command  as  an  argument,
                            you'd write "%%c".

                     %c     This  is  replaced with the named component's com-
                            mand.

                     %m     This is replaced  with  the  final  token  of  the
                            method  name;  if  the  method name has one token,
                            this is identical to %M.

                     %M     This is replaced by the method name; if  the  name
                            consists  of  multiple  tokens, they are joined by
                            space characters.

                     %j     This is replaced by the method name; if  the  name
                            consists  of  multiple  tokens, they are joined by
                            underscores ("_").

                     %t     This is replaced with  the  fully  qualified  type
                            name.

                     %n     This  is  replaced with the name of the instance's
                            private namespace.

                     %s     This is replaced with the  name  of  the  instance
                            command.

                     %w     This is replaced with the original name of the in-
                            stance command; for Snit widgets and widget  adap-
                            tors,  it  will be the Tk window name.  It remains
                            constant, even if the instance command is renamed.

              delegate method * ?to comp? ?using pattern? ?except exceptions?
                     The form delegate method * delegates all  unknown  method
                     names  to the specified component.  The except clause can
                     be used to specify a list  of  exceptions,  i.e.,  method
                     names  that will not be so delegated. The using clause is
                     defined as given above.  In this form, the statement must
                     contain the to clause, the using clause, or both.

                     In  fact,  the  "*"  can  be a list of two or more tokens
                     whose last element is "*", as in the following example:

                         delegate method {tail *} to tail

                     This implicitly defines the method tail whose subcommands
                     will be delegated to the tail component.

              delegate option namespec to comp

              delegate option namespec to comp as target

              delegate option * to comp

              delegate option * to comp except exceptions
                     Defines  a  delegated  option; the namespec is defined as
                     for the option statement.  When  the  configure,  config-
                     urelist,  or  cget  instance method is used to set or re-
                     trieve the option's value, the  equivalent  configure  or
                     cget  command  will be applied to the component as though
                     the  option  was  defined  with  the  following  -config-
                     uremethod and -cgetmethod:

                         method ConfigureMethod {option value} {
                             $comp configure $option $value
                         }

                         method CgetMethod {option} {
                             return [$comp cget $option]
                         }

                     Note  that  delegated options never appear in the options
                     array.

                     If the as clause is specified,  then  the  target  option
                     name is used in place of name.

                     The  form delegate option * delegates all unknown options
                     to the specified component.  The  except  clause  can  be
                     used  to specify a list of exceptions, i.e., option names
                     that will not be so delegated.

                     Warning: options can only be delegated to a component  if
                     it supports the configure and cget instance methods.

                     An  option  cannot be both locally defined and delegated.
                     TBD: Continue from here.

              component comp ?-public method? ?-inherit flag?
                     Explicitly declares a component called comp, and automat-
                     ically defines the component's instance variable.

                     If  the  -public  option is specified, then the option is
                     made public by defining a method  whose  subcommands  are
                     delegated  to  the component e.g., specifying -public my-
                     comp is equivalent to the following:

                         component mycomp
                         delegate method {mymethod *} to mycomp

                     If the -inherit option is specified, then flag must be  a
                     Boolean  value;  if flag is true then all unknown methods
                     and options will be delegated  to  this  component.   The
                     name -inherit implies that instances of this new type in-
                     herit, in a sense, the methods and options of the  compo-
                     nent. That is, -inherit yes is equivalent to:

                         component mycomp
                         delegate option * to mycomp
                         delegate method * to mycomp

              delegate typemethod name to comp ?as target?
                     Delegates  type method name to type component comp.  That
                     is, when type method name is called  on  this  type,  the
                     type method and its arguments will be passed to the named
                     type component's command instead.  That is, the following
                     statement

                         delegate typemethod lostdogs to pound

                     is roughly equivalent to this explicitly defined method:

                         typemethod lostdogs {args} {
                             uplevel $pound lostdogs $args
                         }

                     As  with type methods, the name may have multiple tokens;
                     in this case, the last token of the name is assumed to be
                     the name of the component's method.

                     The  optional  as  clause allows you to specify the dele-
                     gated method name and possibly add some arguments:

                         delegate typemethod lostdogs to pound as "get lostdogs"

              A type method cannot be both locally defined and delegated.

              delegate typemethod name ?to comp? using pattern
                     In this form of the delegate statement, the using  clause
                     is  used  to  specify  the precise form of the command to
                     which type method name name is delegated.  In this  form,
                     the to clause is optional, since the chosen command might
                     not involve any particular type component.

                     The value of the using clause is a list that may  contain
                     any  or  all  of  the following substitution codes; these
                     codes are substituted with the described value  to  build
                     the  delegated  command  prefix.  Note that the following
                     two statements are equivalent:

                         delegate typemethod lostdogs to pound
                         delegate typemethod lostdogs to pound using "%c %m"

                     Each element of the list becomes a single element of  the
                     delegated command--it is never reparsed as a string.

                     Substitutions:

                     %%     This is replaced with a single "%".  Thus, to pass
                            the string "%c" to the  command  as  an  argument,
                            you'd write "%%c".

                     %c     This  is  replaced with the named type component's
                            command.

                     %m     This is replaced with the final token of the  type
                            method  name;  if the type method name has one to-
                            ken, this is identical to %M.

                     %M     This is replaced by the type method name;  if  the
                            name  consists of multiple tokens, they are joined
                            by space characters.

                     %j     This is replaced by the type method name;  if  the
                            name  consists of multiple tokens, they are joined
                            by underscores ("_").

                     %t     This is replaced with  the  fully  qualified  type
                            name.

              delegate  typemethod  * ?to comp? ?using pattern? ?except excep-
              tions?
                     The form delegate typemethod * delegates all unknown type
                     method names to the specified type component.  The except
                     clause can be used to specify a list of exceptions, i.e.,
                     type  method names that will not be so delegated. The us-
                     ing clause is defined as given above.  In this form,  the
                     statement  must  contain the to clause, the using clause,
                     or both.

                     Note: By default, Snit interprets $type foo, where foo is
                     not  a defined type method, as equivalent to $type create
                     foo, where foo is the name of a new instance of the type.
                     If  you  use  delegate typemethod *, then the create type
                     method must always be used explicitly.

                     The "*" can be a list of two or more  tokens  whose  last
                     element is "*", as in the following example:

                         delegate typemethod {tail *} to tail

                     This  implicitly  defines the type method tail whose sub-
                     commands will be delegated to the tail type component.

              typecomponent comp ?-public typemethod? ?-inherit flag?
                     Explicitly declares a type component called comp, and au-
                     tomatically  defines  the  component's  type variable.  A
                     type component is an  arbitrary  command  to  which  type
                     methods  and  instance methods can be delegated; the com-
                     mand's name is stored in a type variable.

                     If the -public option is specified, then the type  compo-
                     nent  is  made public by defining a typemethod whose sub-
                     commands are delegated to the type component, e.g., spec-
                     ifying  -public mytypemethod is equivalent to the follow-
                     ing:

                         typecomponent mycomp
                         delegate typemethod {mytypemethod *} to mycomp

                     If the -inherit option is specified, then flag must be  a
                     Boolean  value;  if  flag  is  true then all unknown type
                     methods will be delegated to this  type  component.  (See
                     the  note  on  "delegate  typemethod *", above.) The name
                     -inherit implies that this type inherits, in a sense, the
                     behavior  of the type component. That is, -inherit yes is
                     equivalent to:

                         typecomponent mycomp
                         delegate typemethod * to mycomp

              pragma ?options...?
                     The pragma statement provides control over how Snit  gen-
                     erates  a  type.  It takes the following options; in each
                     case, flag must be a Boolean  value  recognized  by  Tcl,
                     e.g., 0, 1, yes, no, and so on.

                     By setting the -hastypeinfo, -hastypedestroy, and -hasin-
                     stances pragmas to false and  defining  appropriate  type
                     methods,  you  can create an ensemble command without any
                     extraneous behavior.

                     -canreplace flag
                            If false (the default) Snit will not create an in-
                            stance  of  a snit::type that has the same name as
                            an existing command; this prevents subtle  errors.
                            Setting  this pragma to true restores the behavior
                            of Snit V0.93 and earlier versions.

                     -hastypeinfo flag
                            If true (the default),  the  generated  type  will
                            have  a  type  method called info that is used for
                            type introspection; the info type method is  docu-
                            mented below.  If false, it will not.

                     -hastypedestroy flag
                            If  true  (the  default),  the generated type will
                            have a type method called destroy that is used  to
                            destroy  the  type  and all of its instances.  The
                            destroy  type  method  is  documented  below.   If
                            false, it will not.

                     -hastypemethods flag
                            If  true  (the default), the generated type's type
                            command will have subcommands  (type  methods)  as
                            usual.  If false, the type command will serve only
                            to create instances of the type; the  first  argu-
                            ment is the instance name.

                            This  pragma  and -hasinstances cannot both be set
                            false.

                     -hasinstances flag
                            If true (the default),  the  generated  type  will
                            have  a  type method called create that is used to
                            create instances of the type, along with a variety
                            of  instance-related  features.  If false, it will
                            not.

                            This pragma and -hastypemethods cannot both be set
                            false.

                     -hasinfo flag
                            If  true (the default), instances of the generated
                            type will have an instance method called info that
                            is  used  for  instance  introspection;  the  info
                            method is documented below.   If  false,  it  will
                            not.

                     -simpledispatch flag
                            This  pragma  is intended to make simple, heavily-
                            used abstract data types (e.g., stacks and queues)
                            more efficient.

                            If  false (the default), instance methods are dis-
                            patched normally.  If true, a  faster  dispatching
                            scheme  is  used  instead.   The  speed comes at a
                            price; with -simpledispatch yes you get  the  fol-
                            lowing limitations:

                            o      Methods cannot be delegated.

                            o      uplevel  and upvar do not work as expected:
                                   the caller's scope is two levels up  rather
                                   than one.

                            o      The  option-handling methods (cget, config-
                                   ure, and configurelist) are  very  slightly
                                   slower.

              expose comp

              expose comp as method
                     Deprecated.   To expose component comp publicly, use com-
                     ponent's -public option.

              onconfigure name arglist body
                     Deprecated.  Define option's -configuremethod option  in-
                     stead.

                     As of version 0.95, the following definitions,

                         option -myoption
                         onconfigure -myoption {value} {
                             # Code to save the option's value
                         }

                     are implemented as follows:

                         option -myoption -configuremethod _configure-myoption
                         method _configure-myoption {_option value} {
                             # Code to save the option's value
                         }

              oncget name body
                     Deprecated.  Define option's -cgetmethod option instead.

                     As of version 0.95, the following definitions,

                         option -myoption
                         oncget -myoption {
                             # Code to return the option's value
                         }

                     are implemented as follows:

                         option -myoption -cgetmethod _cget-myoption
                         method _cget-myoption {_option} {
                             # Code to return the option's value
                         }

       snit::widget name definition
              This  command  defines a Snit megawidget type with the specified
              name.   The  definition  is  defined  as  for   snit::type.    A
              snit::widget differs from a snit::type in these ways:

              o      Every  instance  of  a snit::widget has an automatically-
                     created component called hull, which  is  normally  a  Tk
                     frame  widget.   Other  widgets  created  as  part of the
                     megawidget will be created within this widget.

                     The hull component is  initially  created  with  the  re-
                     quested  widget name; then Snit does some magic, renaming
                     the hull component and installing its own  instance  com-
                     mand  in  its  place.   The  hull component's new name is
                     saved in an instance variable called hull.

              o      The name of an instance must be valid Tk window name, and
                     the parent window must exist.

              A  snit::widget definition can include any of statements allowed
              in a snit::type definition, and may also include the following:

              widgetclass name
                     Sets the snit::widget's widget class to name,  overriding
                     the  default.  See The Tk Option Database for more infor-
                     mation.

              hulltype type
                     Determines the kind of widget used as the  snit::widget's
                     hull.  The type may be frame (the default), toplevel, la-
                     belframe; the qualified equivalents of these,  tk::frame,
                     tk::toplevel,  and  tk::labelframe; or, if available, the
                     equivalent Tile widgets: ttk::frame,  ttk::toplevel,  and
                     ttk::labelframe.   In  practice, any widget that supports
                     the -class option can be used as a hull  widget  by  lap-
                     pend'ing its name to the variable snit::hulltypes.

       snit::widgetadaptor name definition
              This  command  defines a Snit megawidget type with the specified
              name.  It differs from snit::widget in that the instance's  hull
              component  is  not  created automatically, but is created in the
              constructor and installed using the installhull  command.   Once
              the  hull  is installed, its instance command is renamed and re-
              placed as with normal snit::widgets.  The  original  command  is
              again accessible in the instance variable hull.

              Note  that  in  general  it is not possible to change the widget
              class of a snit::widgetadaptor's hull widget.

              See The Tk Option Database for  information  on  how  snit::wid-
              getadaptors interact with the option database.

       snit::typemethod type name arglist body
              Defines a new type method (or redefines an existing type method)
              for a previously existing type.

       snit::method type name arglist body
              Defines a new instance method (or redefines an existing instance
              method) for a previously existing type.  Note that delegated in-
              stance methods can't be redefined.

       snit::macro name arglist body
              Defines a Snit macro with the specified name, arglist, and body.
              Macros  are used to define new type and widget definition state-
              ments in terms of the statements defined in this man page.

              A macro is simply a Tcl proc that is defined in the slave inter-
              preter  used  to  compile  type  and  widget definitions.  Thus,
              macros have access to all of  the  type  and  widget  definition
              statements.  See Macros and Meta-programming for more details.

              The  macro  name cannot be the same as any standard Tcl command,
              or any Snit type or widget definition statement, e.g., you can't
              redefine the method or delegate statements, or the standard set,
              list, or string commands.

       snit::compile which type body
              Snit defines a type, widget, or widgetadaptor by "compiling" the
              definition  into  a Tcl script; this script is then evaluated in
              the Tcl interpreter, which actually defines the new type.

              This command exposes the "compiler".  Given  a  definition  body
              for  the named type, where which is type, widget, or widgetadap-
              tor, snit::compile returns a list of two  elements.   The  first
              element  is the fully qualified type name; the second element is
              the definition script.

              snit::compile is useful when additional processing must be  done
              on  the Snit-generated code--if it must be instrumented, for ex-
              ample, or run through the TclDevKit compiler.  In addition,  the
              returned  script could be saved in a ".tcl" file and used to de-
              fine the type as part of an application or library, thus  saving
              the compilation overhead at application start-up.  Note that the
              same version of Snit must be used at  run-time  as  at  compile-
              time.

   THE TYPE COMMAND
       A  type  or  widget definition creates a type command, which is used to
       create instances of the type.  The type command has this form:

       $type typemethod args...
              The typemethod can be any of the Standard  Type  Methods  (e.g.,
              create), or any type method defined in the type definition.  The
              subsequent args depend on the specific typemethod chosen.

              The type command is most often used to create new  instances  of
              the type; hence, the create method is assumed if the first argu-
              ment to the type command doesn't name a valid type  method,  un-
              less  the  type definition includes delegate typemethod * or the
              -hasinstances pragma is set to false.

              Furthermore, if the -hastypemethods pragma is false,  then  Snit
              type  commands  can  be called with no arguments at all; in this
              case, the type command creates an instance with an automatically
              generated name.  In other words, provided that the -hastypemeth-
              ods pragma is false and the type has  instances,  the  following
              commands are equivalent:

              snit::type dog { ... }

              set mydog [dog create %AUTO%]
              set mydog [dog %AUTO%]
              set mydog [dog]

              This doesn't work for Snit widgets, for obvious reasons.

              Snit  1.x  Incompatibility:  In  Snit 1.x, the above behavior is
              available whether  -hastypemethods  is  true  (the  default)  or
              false.

   STANDARD TYPE METHODS
       In  addition to any type methods in the type's definition, all type and
       widget commands will usually have at least the following subcommands:

       $type create name ?option value ...?
              Creates a new instance of the type, giving it the specified name
              and calling the type's constructor.

              For  snit::types, if name is not a fully-qualified command name,
              it is assumed to be a name in the namespace in which the call to
              snit::type  appears.  The method returns the fully-qualified in-
              stance name.

              For snit::widgets and snit::widgetadaptors, name must be a valid
              widget name; the method returns the widget name.

              So  long  as name does not conflict with any defined type method
              name the create keyword may be omitted, unless the type  defini-
              tion  includes delegate typemethod * or the -hasinstances pragma
              is set to false.

              If the name includes the string %AUTO%, it will be replaced with
              the  string  $type$counter  where  $type  is  the  type name and
              $counter is a counter that increments each time %AUTO%  is  used
              for this type.

              By  default,  any arguments following the name will be a list of
              option names and their values; however, a type's constructor can
              specify a different argument list.

              As  of Snit V0.95, create will throw an error if the name is the
              same as any existing command--note that this was always true for
              snit::widgets  and  snit::widgetadaptors.   You  can restore the
              previous behavior using the -canreplace pragma.

       $type info typevars ?pattern?
              Returns a list of the type's type variables (excluding Snit  in-
              ternal variables); all variable names are fully-qualified.

              If  pattern  is given, it's used as a string match pattern; only
              names that match the pattern are returned.

       $type info typemethods ?pattern?
              Returns a list of the names of the  type's type methods.  If the
              type  has  hierarchical type methods, whether locally-defined or
              delegated, only the first word of each will be included  in  the
              list.

              If  the type definition includes delegate typemethod *, the list
              will include only the names of those implicitly  delegated  type
              methods that have been called at least once and are still in the
              type method cache.

              If pattern is given, it's used as a string match  pattern;  only
              names that match the pattern are returned.

       $type info args method
              Returns  a  list  containing  the  names of the arguments to the
              type's method, in order. This method cannot be applied to  dele-
              gated type methods.

       $type info body method
              Returns the body of typemethod method. This method cannot be ap-
              plied to delegated type methods.

       $type info default method aname varname
              Returns a boolean value indicating whether the argument aname of
              the  type's method has a default value (true) or not (false). If
              the argument has a default its value is placed into the variable
              varname.

       $type info instances ?pattern?
              Returns  a  list  of  the type's instances.  For snit::types, it
              will be a list of fully-qualified instance names; for snit::wid-
              gets, it will be a list of Tk widget names.

              If  pattern  is given, it's used as a string match pattern; only
              names that match the pattern are returned.

              Snit 1.x Incompatibility:  In  Snit  1.x,  the  full  multi-word
              names  of  hierarchical  type methods are included in the return
              value.

       $type destroy
              Destroys the type's instances, the  type's  namespace,  and  the
              type command itself.

   THE INSTANCE COMMAND
       A Snit type or widget's create type method creates objects of the type;
       each object has a unique name that is also a Tcl command.  This command
       is used to access the object's methods and data, and has this form:

       $object method args...
              The  method  can be any of the Standard Instance Methods, or any
              instance method defined in the type definition.  The  subsequent
              args depend on the specific method chosen.

   STANDARD INSTANCE METHODS
       In addition to any delegated or locally-defined instance methods in the
       type's definition, all Snit objects will have at  least  the  following
       subcommands:

       $object configure ?option? ?value? ...
              Assigns  new  values to one or more options.  If called with one
              argument, an option name, returns a list describing the  option,
              as Tk widgets do; if called with no arguments, returns a list of
              lists describing all options, as Tk widgets do.

              Warning: This information will be available  for  delegated  op-
              tions  only  if  the component to which they are delegated has a
              configure method that returns this same kind of information.

              Note: Snit defines this method only if the type has at least one
              option.

       $object configurelist optionlist
              Like  configure,  but  takes one argument, a list of options and
              their values.  It's mostly useful in the type  constructor,  but
              can be used anywhere.

              Note: Snit defines this method only if the type has at least one
              option.

       $object cget option
              Returns the option's value.

              Note: Snit defines this method only if the type has at least one
              option.

       $object destroy
              Destroys  the object, calling the destructor and freeing all re-
              lated memory.

              Note: The destroy  method  isn't  defined  for  snit::widget  or
              snit::widgetadaptor objects; instances of these are destroyed by
              calling Tk's destroy command, just as normal widgets are.

       $object info type
              Returns the instance's type.

       $object info vars ?pattern?
              Returns a list of the  object's  instance  variables  (excluding
              Snit internal variables).  The names are fully qualified.

              If  pattern  is given, it's used as a string match pattern; only
              names that match the pattern are returned.

       $object info typevars ?pattern?
              Returns a list of the object's type's type variables  (excluding
              Snit internal variables).  The names are fully qualified.

              If  pattern  is given, it's used as a string match pattern; only
              names that match the pattern are returned.

       $object info typemethods ?pattern?
              Returns a list of the names of the  type's type methods.  If the
              type  has  hierarchical type methods, whether locally-defined or
              delegated, only the first word of each will be included  in  the
              list.

              If  the type definition includes delegate typemethod *, the list
              will include only the names of those implicitly  delegated  type
              methods that have been called at least once and are still in the
              type method cache.

              If pattern is given, it's used as a string match  pattern;  only
              names that match the pattern are returned.

              Snit  1.x  Incompatibility:   In  Snit  1.x, the full multi-word
              names of hierarchical type methods are included  in  the  return
              value.

       $object info options ?pattern?
              Returns  a  list  of the object's option names.  This always in-
              cludes local options and explicitly delegated options.   If  un-
              known  options  are  delegated  as well, and if the component to
              which they are delegated responds to $object configure  like  Tk
              widgets  do,  then  the result will include all possible unknown
              options that can be delegated to the component.

              If pattern is given, it's used as a string match  pattern;  only
              names that match the pattern are returned.

              Note  that the return value might be different for different in-
              stances of the same type, if component  object  types  can  vary
              from one instance to another.

       $object info methods ?pattern?
              Returns  a  list of the names of the instance's methods.  If the
              type has hierarchical methods, whether locally-defined or  dele-
              gated, only the first word of each will be included in the list.

              If the type definition includes delegate method *, the list will
              include only the names of  those  implicitly  delegated  methods
              that  have been called at least once and are still in the method
              cache.

              If pattern is given, it's used as a string match  pattern;  only
              names that match the pattern are returned.

              Snit  1.x  Incompatibility:   In  Snit  1.x, the full multi-word
              names of hierarchical type methods are included  in  the  return
              value.

       $object info args method
              Returns  a list containing the names of the arguments to the in-
              stance's method, in order. This method cannot be applied to del-
              egated methods.

       $object info body method
              Returns  the  body  of the instance's method method. This method
              cannot be applied to delegated methods.

       $object info default method aname varname
              Returns a boolean value indicating whether the argument aname of
              the instance's method has a default value (true) or not (false).
              If the argument has a default its value is placed into the vari-
              able varname.

   COMMANDS FOR USE IN OBJECT CODE
       Snit  defines  the following commands for use in your object code: that
       is, for use in type methods, instance methods,  constructors,  destruc-
       tors,  onconfigure  handlers,  oncget handlers, and procs.  They do not
       reside in the ::snit:: namespace; instead, they are  created  with  the
       type, and can be used without qualification.

       mymethod name ?args...?
              The mymethod command is used for formatting callback commands to
              be passed to other objects.  It  returns  a  command  that  when
              called  will  invoke  method  name with the specified arguments,
              plus of course any arguments added  by  the  caller.   In  other
              words,  both  of  the following commands will cause the object's
              dosomething method to be called when the $button is pressed:

                  $button configure -command [list $self dosomething myargument]

                  $button configure -command [mymethod dosomething myargument]

              The chief distinction between the two is that  the  latter  form
              will not break if the object's command is renamed.

       mytypemethod name ?args...?
              The  mytypemethod  command  is used for formatting callback com-
              mands to be passed to other objects.  It returns a command  that
              when  called will invoke type method name with the specified ar-
              guments, plus of course any arguments added by the  caller.   In
              other  words,  both of the following commands will cause the ob-
              ject's dosomething type method to  be  called  when  $button  is
              pressed:

                  $button configure -command [list $type dosomething myargument]

                  $button configure -command [mytypemethod dosomething myargument]

              Type  commands  cannot be renamed, so in practice there's little
              difference between the two forms.  mytypemethod is provided  for
              parallelism with mymethod.

       myproc name ?args...?
              The  myproc  command is used for formatting callback commands to
              be passed to other objects.  It  returns  a  command  that  when
              called  will  invoke the type proc name with the specified argu-
              ments, plus of course any arguments added  by  the  caller.   In
              other  words,  both of the following commands will cause the ob-
              ject's dosomething proc to be called when $button is pressed:

                  $button configure -command [list ${type}::dosomething myargument]

                  $button configure -command [myproc dosomething myargument]

       myvar name
              Given an instance variable name,  returns  the  fully  qualified
              name.  Use this if you're passing the variable to some other ob-
              ject, e.g., as a -textvariable to a Tk label widget.

       mytypevar name
              Given an type variable name, returns the fully  qualified  name.
              Use  this  if  you're passing the variable to some other object,
              e.g., as a -textvariable to a Tk label widget.

       from argvName option ?defvalue?
              The from command plucks an option value from a list  of  options
              and  their  values, such as is passed into a type's constructor.
              argvName must be the name of a variable containing such a  list;
              option is the name of the specific option.

              from  looks  for  option in the option list.  If it is found, it
              and its value are removed from the list, and the  value  is  re-
              turned.  If option doesn't appear in the list, then the defvalue
              is returned.  If the option is locally-defined option, and  def-
              value is not specified, then the option's default value as spec-
              ified in the type definition will be returned instead.

       install compName using objType objName args...
              Creates a new object of type objType called objName and installs
              it as component compName, as described in Components and Delega-
              tion.  Any additional args... are passed along with the name  to
              the  objType command.  If this is a snit::type, then the follow-
              ing two commands are equivalent:

                  install myComp using myObjType $self.myComp args...

                  set myComp [myObjType $self.myComp args...]

              Note that whichever method is used, compName must still  be  de-
              clared in the type definition using component, or must be refer-
              enced in at least one delegate statement.

              If this is a snit::widget or snit::widgetadaptor, and if options
              have  been  delegated  to component compName, then those options
              will receive default values from the Tk option  database.   Note
              that  it doesn't matter whether the component to be installed is
              a widget or not.  See The Tk Option Database for  more  informa-
              tion.

              install  cannot  be used to install type components; just assign
              the type component's command name to the type component's  vari-
              able instead.

       installhull using widgetType args...

       installhull name
              The constructor of a snit::widgetadaptor must create a widget to
              be the object's hull component; the widget is installed  as  the
              hull component using this command.  Note that the installed wid-
              get's name must be $win.  This command has two forms.

              The first form specifies the widgetType and the  args...   (that
              is,  the  hardcoded  option  list)  to use in creating the hull.
              Given this form, installhull creates the hull widget,  and  ini-
              tializes  any  options  delegated to the hull from the Tk option
              database.

              In the second form, the hull widget has  already  been  created;
              note  that its name must be "$win".  In this case, the Tk option
              database is not queried for any options delegated to  the  hull.
              The  longer  form is preferred; however, the shorter form allows
              the programmer to adapt a widget  created  elsewhere,  which  is
              sometimes useful.  For example, it can be used to adapt a "page"
              widget created by a BWidgets tabbed notebook  or  pages  manager
              widget.

              See The Tk Option Database for more information about snit::wid-
              getadaptors and the option database.

       variable name
              Normally, instance variables are defined in the type  definition
              along  with  the  options,  methods, and so forth; such instance
              variables are automatically visible in all instance code  (e.g.,
              method  bodies).   However,  instance  code can use the variable
              command to declare instance variables that don't appear  in  the
              type  definition,  and  also to bring variables from other name-
              spaces into scope in the usual way.

              It's generally clearest to define all instance variables in  the
              type  definition,  and  omit  declaring  them  in methods and so
              forth.

              Note that this is an instance-specific version of  the  standard
              Tcl ::variable command.

       typevariable name
              Normally,  type  variables  are  defined in the type definition,
              along with the instance variables; such type variables are auto-
              matically  visible  in  all  of  the type's code.  However, type
              methods, instance methods and so forth can use  typevariable  to
              declare type variables that don't appear in the type definition.

              It's  generally  clearest  to  declare all type variables in the
              type definition, and omit declaring them in methods, type  meth-
              ods, etc.

       varname name
              Deprecated.  Use myvar instead.

              Given  an  instance  variable  name, returns the fully qualified
              name.  Use this if you're passing the variable to some other ob-
              ject, e.g., as a -textvariable to a Tk label widget.

       typevarname name
              Deprecated.  Use mytypevar instead.

              Given  a  type  variable name, returns the fully qualified name.
              Use this if you're passing the type variable to some  other  ob-
              ject, e.g., as a -textvariable to a Tk label widget.

       codename name
              Deprecated.   Use myproc instead.  Given the name of a proc (but
              not a type or instance method), returns the fully-qualified com-
              mand name, suitable for passing as a callback.

   COMPONENTS AND DELEGATION
       When  an object includes other objects, as when a toolbar contains but-
       tons or a GUI object contains an object that references a database, the
       included object is called a component.  The standard way to handle com-
       ponent objects owned by a Snit object is to declare them  using  compo-
       nent,  which  creates  a component instance variable.  In the following
       example, a dog object has a tail object:

                  snit::type dog {
                      component mytail

                      constructor {args} {
                          set mytail [tail %AUTO% -partof $self]
                          $self configurelist $args
                      }

                      method wag {} {
                          $mytail wag
                      }
                  }

                  snit::type tail {
                      option -length 5
                      option -partof
                      method wag {} { return "Wag, wag, wag."}
                  }

       Because the tail object's name is stored in an instance variable,  it's
       easily accessible in any method.

       The install command provides an alternate way to create and install the
       component:

                  snit::type dog {
                      component mytail

                      constructor {args} {
                          install mytail using tail %AUTO% -partof $self
                          $self configurelist $args
                      }

                      method wag {} {
                          $mytail wag
                      }
                  }

       For snit::types, the two methods are equivalent; for snit::widgets  and
       snit::widgetadaptors, the install command properly initializes the wid-
       get's options by querying The Tk Option Database.

       In the above examples, the dog object's wag  method  simply  calls  the
       tail  component's wag method.  In OO jargon, this is called delegation.
       Snit provides an easier way to do this:

                  snit::type dog {
                      delegate method wag to mytail

                      constructor {args} {
                          install mytail using tail %AUTO% -partof $self
                          $self configurelist $args
                      }
                  }

       The delegate statement in the type definition  implicitly  defines  the
       instance variable mytail to hold the component's name (though it's good
       form to use component to declare it explicitly); it  also  defines  the
       dog object's wag method, delegating it to the mytail component.

       If  desired,  all  otherwise unknown methods can be delegated to a spe-
       cific component:

                  snit::type dog {
                delegate method * to mytail

                constructor {args} {
                    set mytail [tail %AUTO% -partof $self]
                    $self configurelist $args
                }

                method bark { return "Bark, bark, bark!" }
                  }

       In this case, a dog object will handle its own  bark  method;  but  wag
       will  be passed along to mytail.  Any other method, being recognized by
       neither dog nor tail, will simply raise an error.

       Option delegation is similar to method delegation, except for  the  in-
       teractions with the Tk option database; this is described in The Tk Op-
       tion Database.

   TYPE COMPONENTS AND DELEGATION
       The relationship between type components  and  instance  components  is
       identical  to  that  between type variables and instance variables, and
       that between type methods and instance methods.  Just  as  an  instance
       component  is an instance variable that holds the name of a command, so
       a type component is a type variable that holds the name of  a  command.
       In  essence, a type component is a component that's shared by every in-
       stance of the type.

       Just as delegate method can be used to  delegate  methods  to  instance
       components,  as  described  in  Components  and Delegation, so delegate
       typemethod can be used to delegate type methods to type components.

       Note also that as of Snit 0.95 delegate method can delegate methods  to
       both instance components and type components.

   THE TK OPTION DATABASE
       This  section describes how Snit interacts with the Tk option database,
       and assumes the reader has a working knowledge of the  option  database
       and its uses.  The book Practical Programming in Tcl and Tk by Welch et
       al has a good introduction to the option database,  as  does  Effective
       Tcl/Tk Programming.

       Snit  is  implemented  so  that  most of the time it will simply do the
       right thing with respect to the option database, provided that the wid-
       get  developer  does the right thing by Snit.  The body of this section
       goes into great deal about what Snit  requires.   The  following  is  a
       brief statement of the requirements, for reference.

       o      If  the  snit::widget's  default widget class is not what is de-
              sired, set it explicitly using widgetclass in the widget defini-
              tion.

       o      When  defining  or  delegating options, specify the resource and
              class names explicitly when if  the  defaults  aren't  what  you
              want.

       o      Use  installhull using to install the hull for snit::widgetadap-
              tors.

       o      Use install to install all other components.

       The interaction of Tk widgets with the option  database  is  a  complex
       thing;  the  interaction  of Snit with the option database is even more
       so, and repays attention to detail.

       Setting the widget class: Every Tk widget has a widget class.   For  Tk
       widgets, the widget class name is the just the widget type name with an
       initial capital letter, e.g., the widget class for  button  widgets  is
       "Button".

       Similarly,  the widget class of a snit::widget defaults to the unquali-
       fied type name with the first letter  capitalized.   For  example,  the
       widget class of

                  snit::widget ::mylibrary::scrolledText { ... }

       is  "ScrolledText".   The widget class can also be set explicitly using
       the widgetclass statement within the snit::widget definition.

       Any widget can be used as the hulltype provided that  it  supports  the
       -class  option  for changing its widget class name.  See the discussion
       of the hulltype command, above.  The user may pass -class to the widget
       at instantion.

       The  widget  class of a snit::widgetadaptor is just the widget class of
       its hull widget; this cannot be changed unless the hull widget supports
       -class, in which case it will usually make more sense to use snit::wid-
       get rather than snit::widgetadaptor.

       Setting option resource names and classes:  In  Tk,  every  option  has
       three  names:  the  option name, the resource name, and the class name.
       The option name begins with a hyphen and is all  lowercase;  it's  used
       when creating widgets, and with the configure and cget commands.

       The resource and class names are used to initialize option default val-
       ues by querying the Tk option database.  The resource name  is  usually
       just  the  option name minus the hyphen, but may contain uppercase let-
       ters at word boundaries; the class name is usually  just  the  resource
       name  with  an  initial capital, but not always.  For example, here are
       the option, resource, and class names for several text widget options:

                  -background         background         Background
                  -borderwidth        borderWidth        BorderWidth
                  -insertborderwidth  insertBorderWidth  BorderWidth
                  -padx               padX               Pad

       As is easily seen, sometimes the resource and class names  can  be  in-
       ferred from the option name, but not always.

       Snit  options  also have a resource name and a class name.  By default,
       these names follow the rule given above: the resource name is  the  op-
       tion  name  without the hyphen, and the class name is the resource name
       with an initial capital.  This is true for both locally-defined options
       and explicitly delegated options:

                  snit::widget mywidget {
                      option -background
                      delegate option -borderwidth to hull
                      delegate option * to text
                # ...
                  }

       In  this case, the widget class name is "Mywidget".  The widget has the
       following options: -background, which is locally defined, and  -border-
       width,  which  is explicitly delegated; all other widgets are delegated
       to a component called "text", which is probably a Tk text  widget.   If
       so,  mywidget  has  all the same options as a text widget.  The option,
       resource, and class names are as follows:

                  -background  background  Background
                  -borderwidth borderwidth Borderwidth
                  -padx        padX        Pad

       Note that the locally defined option, -background, happens to have  the
       same three names as the standard Tk -background option; and -pad, which
       is delegated implicitly to the text component, has the same three names
       for  mywidget  as  it  does  for the text widget.  -borderwidth, on the
       other hand, has different resource and class names than usual,  because
       the  internal  word  "width"  isn't  capitalized.   For consistency, it
       should be; this is done as follows:

                  snit::widget mywidget {
                option -background
                delegate option {-borderwidth borderWidth} to hull
                delegate option * to text
                # ...
                  }

       The class name will default to "BorderWidth", as expected.

       Suppose, however, that mywidget also delegated -padx and -pady  to  the
       hull.   In this case, both the resource name and the class name must be
       specified explicitly:

                  snit::widget mywidget {
                option -background
                delegate option {-borderwidth borderWidth} to hull
                delegate option {-padx padX Pad} to hull
                delegate option {-pady padY Pad} to hull
                delegate option * to text
                # ...
                  }

       Querying the option database: If you set your  widgetclass  and  option
       names as described above, Snit will query the option database when each
       instance is created, and will generally do  the  right  thing  when  it
       comes  to  querying the option database.  The remainder of this section
       goes into the gory details.

       Initializing locally defined options: When an instance of a  snit::wid-
       get is created, its locally defined options are initialized as follows:
       each option's resource and class names are used to query the Tk  option
       database.   If  the result is non-empty, it is used as the option's de-
       fault; otherwise, the default hardcoded in the type definition is used.
       In either case, the default can be overridden by the caller.  For exam-
       ple,

                  option add *Mywidget.texture pebbled

                  snit::widget mywidget {
                option -texture smooth
                # ...
                  }

                  mywidget .mywidget -texture greasy

       Here, -texture would normally default to "smooth", but because  of  the
       entry  added to the option database it defaults to "pebbled".  However,
       the caller has explicitly overridden the default, and so the new widget
       will be "greasy".

       Initializing  options delegated to the hull: A snit::widget's hull is a
       widget, and given that its class has been set it is expected  to  query
       the  option  database  for itself.  The only exception concerns options
       that are delegated to it with a different name.  Consider the following
       code:

                  option add *Mywidget.borderWidth 5
                  option add *Mywidget.relief sunken
                  option add *Mywidget.hullbackground red
                  option add *Mywidget.background green

                  snit::widget mywidget {
                delegate option -borderwidth to hull
                delegate option -hullbackground to hull as -background
                delegate option * to hull
                # ...
                  }

                  mywidget .mywidget

                  set A [.mywidget cget -relief]
                  set B [.mywidget cget -hullbackground]
                  set C [.mywidget cget -background]
                  set D [.mywidget cget -borderwidth]

       The question is, what are the values of variables A, B, C and D?

       The value of A is "sunken".  The hull is a Tk frame that has been given
       the widget class "Mywidget"; it will  automatically  query  the  option
       database  and  pick up this value.  Since the -relief option is implic-
       itly delegated to the hull, Snit takes no action.

       The value of B is "red".  The hull will automatically pick up the value
       "green"  for  its  -background option, just as it picked up the -relief
       value.  However, Snit knows  that  -hullbackground  is  mapped  to  the
       hull's  -background  option;  hence, it queries the option database for
       -hullbackground and gets "red" and updates the hull accordingly.

       The value of C is also "red", because -background is  implicitly  dele-
       gated to the hull; thus, retrieving it is the same as retrieving -hull-
       background.  Note that this case is unusual; in  practice,  -background
       would probably be explicitly delegated to some other component.

       The  value of D is "5", but not for the reason you think.  Note that as
       it is defined above, the resource name  for  -borderwidth  defaults  to
       "borderwidth",  whereas the option database entry is "borderWidth".  As
       with -relief, the hull picks up its own -borderwidth option before Snit
       does  anything.   Because  the  option is delegated under its own name,
       Snit assumes that the correct thing has  happened,  and  doesn't  worry
       about it any further.

       For  snit::widgetadaptors,  the case is somewhat altered.  Widget adap-
       tors retain the widget class of their hull, and the hull is not created
       automatically  by Snit.  Instead, the snit::widgetadaptor must call in-
       stallhull in its constructor.  The normal way to do this is as follows:

                  snit::widgetadaptor mywidget {
                # ...
                constructor {args} {
                    # ...
                    installhull using text -foreground white
                    #
                }
                #...
                  }

       In this case, the installhull command will create the hull using a com-
       mand like this:

                  set hull [text $win -foreground white]

       The hull is a text widget, so its widget class is "Text".  Just as with
       snit::widget hulls, Snit assumes that it will pick up all of its normal
       option  values  automatically;  options delegated from a different name
       are initialized from the option database in the same way.

       Initializing options delegated to other components: Non-hull components
       are  matched  against the option database in two ways.  First, a compo-
       nent widget remains a widget still, and therefore is  initialized  from
       the  option  database in the usual way.  Second, the option database is
       queried for all options delegated to the component, and  the  component
       is  initialized  accordingly--provided that the install command is used
       to create it.

       Before option database support was added to Snit, the usual way to cre-
       ate  a  component was to simply create it in the constructor and assign
       its command name to the component variable:

                  snit::widget mywidget {
                delegate option -background to myComp

                constructor {args} {
                    set myComp [text $win.text -foreground black]
                }
                  }

       The drawback of this method is that Snit has no opportunity to initial-
       ize the component properly.  Hence, the following approach is now used:

                  snit::widget mywidget {
                delegate option -background to myComp

                constructor {args} {
                    install myComp using text $win.text -foreground black
                }
                  }

       The install command does the following:

       o      Builds  a list of the options explicitly included in the install
              command -- in this case, -foreground.

       o      Queries the option database for all options delegated explicitly
              to the named component.

       o      Creates the component using the specified command, after insert-
              ing into it a list of options and values read  from  the  option
              database.   Thus,  the explicitly included options (-foreground)
              will override anything read from the option database.

       o      If the widget definition implicitly  delegated  options  to  the
              component  using  delegate  option  *, then Snit calls the newly
              created component's configure method to receive a list of all of
              the  component's  options.   From this Snit builds a list of op-
              tions implicitly delegated to the component that  were  not  ex-
              plicitly included in the install command.  For all such options,
              Snit queries the option database and  configures  the  component
              accordingly.

       Non-widget  components:  The  option  database  is  never  queried  for
       snit::types, since it can only be queried given a Tk widget name.  How-
       ever, snit::widgets can have non-widget components.  And if options are
       delegated to those components, and if the install command  is  used  to
       install those components, then they will be initialized from the option
       database just as widget components are.

   MACROS AND META-PROGRAMMING
       The snit::macro command enables a certain  amount  of  meta-programming
       with Snit classes.  For example, suppose you like to define properties:
       instance variables that have set/get methods.   Your  code  might  look
       like this:

                  snit::type dog {
                      variable mood happy

                      method getmood {} {
                          return $mood
                      }

                      method setmood {newmood} {
                          set mood $newmood
                      }
                  }

       That's  nine lines of text per property.  Or, you could define the fol-
       lowing snit::macro:

                  snit::macro property {name initValue} {
                      variable $name $initValue

                      method get$name {} "return $name"

                      method set$name {value} "set $name \$value"
                  }

       Note that a snit::macro is just a normal Tcl proc defined in the  slave
       interpreter  used  to compile type and widget definitions; as a result,
       it has access to all the commands used to define types and widgets.

       Given this new macro, you can define a property in one line of code:

                  snit::type dog {
                      property mood happy
                  }

       Within a macro, the commands variable and proc refer to the Snit  type-
       definition  commands,  not the standard Tcl commands.  To get the stan-
       dard Tcl commands, use _variable and _proc.

       Because a single slave interpreter is used for compiling all Snit types
       and  widgets  in the application, there's the possibility of macro name
       collisions.  If you're writing a reuseable package using Snit, and  you
       use some snit::macros, define them in your package namespace:

                  snit::macro mypkg::property {name initValue} { ... }

                  snit::type dog {
                      mypkg::property mood happy
                  }

       This leaves the global namespace open for application authors.

   VALIDATION TYPES
       A  validation type is an object that can be used to validate Tcl values
       of a particular kind.  For example, snit::integer is used  to  validate
       that a Tcl value is an integer.

       Every  validation  type  has  a validate method which is used to do the
       validation. This method must take a single argument, the  value  to  be
       validated; further, it must do nothing if the value is valid, but throw
       an error if the value is invalid:

                  snit::integer validate 5     ;# Does nothing
                  snit::integer validate 5.0   ;# Throws an error (not an integer!)

       The validate method will always return the validated value on  success,
       and throw the -errorcode INVALID on error.

       Snit defines a family of validation types, all of which are implemented
       as snit::type's.  They can be used as is; in addition, their  instances
       serve  as parameterized subtypes.  For example, a probability is a num-
       ber between 0.0 and 1.0 inclusive:

                  snit::double probability -min 0.0 -max 1.0

       The example above creates an  instance  of  snit::double--a  validation
       subtype--called  probability, which can be used to validate probability
       values:

                  probability validate 0.5   ;# Does nothing
                  probability validate 7.9   ;# Throws an error

       Validation subtypes can be defined explicitly, as in the above example;
       when  a  locally-defined  option's -type is specified, they may also be
       created on the fly:

                  snit::enum ::dog::breed -values {mutt retriever sheepdog}

                  snit::type dog {
                      # Define subtypes on the fly...
                      option -breed -type {
                          snit::enum -values {mutt retriever sheepdog}
                      }

                      # Or use predefined subtypes...
                      option -breed -type ::dog::breed
                  }

       Any object that has a validate  method  with  the  semantics  described
       above  can  be used as a validation type; see Defining Validation Types
       for information on how to define new ones.

       Snit defines the following validation types:

       snit::boolean validate ?value?

       snit::boolean name
              Validates Tcl boolean values: 1, 0,  on,  off,  yes,  no,  true,
              false.  It's possible to define subtypes--that is, instances--of
              snit::boolean, but as it has no options there's no reason to  do
              so.

       snit::double validate ?value?

       snit::double name ?option value...?
              Validates  floating-point  values.  Subtypes may be created with
              the following options:

              -min min
                     Specifies a floating-point minimum bound; a value is  in-
                     valid if it is strictly less than min.

              -max max
                     Specifies  a floating-point maximum bound; a value is in-
                     valid if it is strictly greater than max.

       snit::enum validate ?value?

       snit::enum name ?option value...?
              Validates that a value comes from an enumerated list.  The  base
              type  is of little use by itself, as only subtypes actually have
              an enumerated list to validate against.  Subtypes may be created
              with the following options:

              -values list
                     Specifies  a  list  of valid values.  A value is valid if
                     and only if it's included in the list.

       snit::fpixels validate ?value?

       snit::fpixels name ?option value...?
              Tk programs only. Validates screen  distances,  in  any  of  the
              forms  accepted  by  winfo fpixels. Subtypes may be created with
              the following options:

              -min min
                     Specifies a minimum bound; a value is invalid  if  it  is
                     strictly  less  than  min.  The bound may be expressed in
                     any of the forms accepted by winfo fpixels.

              -max max
                     Specifies a maximum bound; a value is invalid  if  it  is
                     strictly greater than max.  The bound may be expressed in
                     any of the forms accepted by winfo fpixels.

       snit::integer validate ?value?

       snit::integer name ?option value...?
              Validates integer values.  Subtypes may be created with the fol-
              lowing options:

              -min min
                     Specifies an integer minimum bound; a value is invalid if
                     it is strictly less than min.

              -max max
                     Specifies an integer maximum bound; a value is invalid if
                     it is strictly greater than max.

       snit::listtype validate ?value?

       snit::listtype name ?option value...?
              Validates  Tcl lists. Subtypes may be created with the following
              options:

              -minlen min
                     Specifies a minimum list length; the value is invalid  if
                     it has fewer than min elements.  Defaults to 0.

              -maxlen max
                     Specifies  a maximum list length; the value is invalid if
                     it more than max elements.

              -type type
                     Specifies the type of the list elements; type must be the
                     name  of  a validation type or subtype.  In the following
                     example, the value of -numbers must be a  list  of  inte-
                     gers.

                         option -numbers -type {snit::listtype -type snit::integer}

                     Note  that this option doesn't support defining new vali-
                     dation subtypes on the fly; that is, the  following  code
                     will not work (yet, anyway):

                         option -numbers -type {
                             snit::listtype -type {snit::integer -min 5}
                         }

                     Instead, define the subtype explicitly:

                         snit::integer gt4 -min 5

                         snit::type mytype {
                             option -numbers -type {snit::listtype -type gt4}
                         }

       snit::pixels validate ?value?

       snit::pixels name ?option value...?
              Tk  programs  only.  Validates  screen  distances, in any of the
              forms accepted by winfo pixels. Subtypes may be created with the
              following options:

              -min min
                     Specifies  a  minimum  bound; a value is invalid if it is
                     strictly less than min.  The bound may  be  expressed  in
                     any of the forms accepted by winfo pixels.

              -max max
                     Specifies  a  maximum  bound; a value is invalid if it is
                     strictly greater than max.  The bound may be expressed in
                     any of the forms accepted by winfo pixels.

       snit::stringtype validate ?value?

       snit::stringtype name ?option value...?
              Validates Tcl strings. The base type is of little use by itself,
              since very Tcl value is also a valid string.   Subtypes  may  be
              created with the following options:

              -minlen min
                     Specifies  a  minimum string length; the value is invalid
                     if it has fewer than min characters.  Defaults to 0.

              -maxlen max
                     Specifies a maximum string length; the value  is  invalid
                     if it has more than max characters.

              -glob pattern
                     Specifies a string match pattern; the value is invalid if
                     it doesn't match the pattern.

              -regexp regexp
                     Specifies a regular expression; the value is  invalid  if
                     it doesn't match the regular expression.

              -nocase flag
                     By  default, both -glob and -regexp matches are case-sen-
                     sitive.  If -nocase is set to true, then both  -glob  and
                     -regexp matches are case-insensitive.

       snit::window validate ?value?

       snit::window name
              Tk  programs  only.   Validates Tk window names.  The value must
              cause winfo exists to return true; otherwise, the value  is  in-
              valid.  It's possible to define subtypes--that is, instances--of
              snit::window, but as it has no options  at  present  there's  no
              reason to do so.

   DEFINING VALIDATION TYPES
       There  are  three ways to define a new validation type: as a subtype of
       one of Snit's validation types, as a validation type command, and as  a
       full-fledged validation type similar to those provided by Snit.  Defin-
       ing subtypes of Snit's validation types is described above, under Vali-
       dation Types.

       The  next  simplest way to create a new validation type is as a valida-
       tion type command.  A validation type is simply an object  that  has  a
       validate  method;  the validate method must take one argument, a value,
       return the value if it is valid, and throw an error with -errorcode IN-
       VALID  if  the  value is invalid.  This can be done with a simple proc.
       For example, the snit::boolean validate type  could  have  been  imple-
       mented like this:

                  proc ::snit::boolean {"validate" value} {
                      if {![string is boolean -strict $value]} {
                          return -code error -errorcode INVALID  "invalid boolean \"$value\", should be one of: 1, 0, ..."
                      }

                      return $value
                  }

       A  validation  type  defined in this way cannot be subtyped, of course;
       but for many applications this will be sufficient.

       Finally, one can define a full-fledged, subtype-able validation type as
       a snit::type.  Here's a skeleton to get you started:

                  snit::type myinteger {
                      # First, define any options you'd like to use to define
                      # subtypes.  Give them defaults such that they won't take
                      # effect if they aren't used, and marked them "read-only".
                      # After all, you shouldn't be changing their values after
                      # a subtype is defined.
                      #
                      # For example:

                      option -min -default "" -readonly 1
                      option -max -default "" -readonly 1

                      # Next, define a "validate" type method which should do the
                      # validation in the basic case.  This will allow the
                      # type command to be used as a validation type.

                      typemethod validate {value} {
                          if {![string is integer -strict $value]} {
                              return -code error -errorcode INVALID  "invalid value \"$value\", expected integer"
                          }

                          return $value
                      }

                      # Next, the constructor should validate the subtype options,
                      # if any.  Since they are all readonly, we don't need to worry
                      # about validating the options on change.

                      constructor {args} {
                          # FIRST, get the options
                          $self configurelist $args

                          # NEXT, validate them.

                          # I'll leave this to your imagination.
                      }

                      # Next, define a "validate" instance method; its job is to
                      # validate values for subtypes.

                      method validate {value} {
                          # First, call the type method to do the basic validation.
                          $type validate $value

                          # Now we know it's a valid integer.

                          if {("" != $options(-min) && $value < $options(-min))  ||
                              ("" != $options(-max) && $value > $options(-max))} {
                              # It's out of range; format a detailed message about
                              # the error, and throw it.

                              set msg "...."

                              return -code error -errorcode INVALID $msg
                          }

                          # Otherwise, if it's valid just return it.
                          return $valid
                      }
                  }

       And now you have a type that can be subtyped.

       The  file "validate.tcl" in the Snit distribution defines all of Snit's
       validation  types;  you  can  find  the  complete  implementation   for
       snit::integer  and  the  other types there, to use as examples for your
       own types.

CAVEATS
       If you have problems, find bugs, or new ideas you are hereby  cordially
       invited  to  submit a report of your problem, bug, or idea as explained
       in the section Bugs, Ideas, Feedback below.

       Additionally, you might  wish  to  join  the  Snit  mailing  list;  see
       http://www.wjduquette.com/snit for details.

       One  particular  area  to  watch  is using snit::widgetadaptor to adapt
       megawidgets created by other megawidget packages;  correct  widget  de-
       struction  depends  on the order of the <Destroy> bindings.  The wisest
       course is simply not to do this.

KNOWN BUGS
       o      Error stack traces returned by Snit 1.x are extremely  ugly  and
              typically contain far too much information about Snit internals.
              The error messages are much improved in Snit 2.2.

       o      Also see the Project Trackers as explained in the section  Bugs,
              Ideas, Feedback below.

HISTORY
       During   the   course  of  developing  Notebook  (See  http://www.wjdu-
       quette.com/notebook), my Tcl-based  personal  notebook  application,  I
       found  I was writing it as a collection of objects.  I wasn't using any
       particular object-oriented framework; I was  just  writing  objects  in
       pure  Tcl  following the guidelines in my Guide to Object Commands (see
       http://www.wjduquette.com/tcl/objects.html), along  with  a  few  other
       tricks I'd picked up since.  And though it was working well, it quickly
       became tiresome because of the amount of  boilerplate  code  associated
       with each new object type.

       So  that  was one thing--tedium is a powerful motivator.  But the other
       thing I noticed is that I wasn't using inheritance at all, and I wasn't
       missing  it.   Instead,  I  was  using delegation: objects that created
       other objects and delegated methods to them.

       And I said to myself, "This is getting tedious...there has got to be  a
       better  way."  And one afternoon, on a whim, I started working on Snit,
       an object system that works the way Tcl works.   Snit  doesn't  support
       inheritance, but it's great at delegation, and it makes creating megaw-
       idgets easy.

       If you have any comments or suggestions (or bug reports!)  don't  hesi-
       tate  to send me e-mail at will@wjduquette.com.  In addition, there's a
       Snit mailing list; you can find out more about it at the Snit home page
       (see http://www.wjduquette.com/snit).

CREDITS
       Snit has been designed and implemented from the very beginning by Will-
       iam H. Duquette.  However, much credit belongs to the following  people
       for using Snit and providing me with valuable feedback: Rolf Ade, Colin
       McCormack, Jose Nazario, Jeff Godfrey, Maurice Diamanti, Egon  Pasztor,
       David  S. Cargo, Tom Krehbiel, Michael Cleverly, Andreas Kupries, Marty
       Backe, Andy Goth, Jeff Hobbs,  Brian  Griffin,  Donal  Fellows,  Miguel
       Sofer,  Kenneth  Green, and Anton Kovalenko.  If I've forgotten anyone,
       my apologies; let me know and I'll add your name to the list.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will  undoubtedly  contain
       bugs  and  other  problems.  Please report such in the category snit of
       the  Tcllib  Trackers  [http://core.tcl.tk/tcllib/reportlist].   Please
       also  report any ideas for enhancements you may have for either package
       and/or documentation.

       When proposing code changes, please provide unified diffs, i.e the out-
       put of diff -u.

       Note  further  that  attachments  are  strongly  preferred over inlined
       patches. Attachments can be made by going  to  the  Edit  form  of  the
       ticket  immediately  after  its  creation, and then using the left-most
       button in the secondary navigation bar.

KEYWORDS
       BWidget, C++, Incr Tcl, Snit, adaptors, class, mega widget, object, ob-
       ject oriented, type, widget, widget adaptors

CATEGORY
       Programming tools

COPYRIGHT
       Copyright (c) 2003-2009, by William H. Duquette

tcllib                               2.3.2                          snit(3tcl)

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