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



______________________________________________________________________________

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
       applications 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
       object, 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
       difference 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
                     optionally 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
                     command, 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
                     variables 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 possible 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 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.

              Snit 1.x Incompatibility: In Snit 1.x, the following following
              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
                     addition, 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
                     command in Tcl 8.5.

              variable name ?-array? ?value?
                     Defines an instance variable, a private variable
                     associated 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
                     locally 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 possible 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
              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 following
              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
                     optionally gives it an initial value.  The initial value
                     defaults to the empty string if no defaultValue is
                     specified.

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

                     The namespec is a list defining the option's name,
                     resource 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 resource
              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.,
              -configuremethod), 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
                            configurelist at creation time, i.e., in the
                            type's constructor.

                     -type type
                            Every locally-defined option may define its
                            validation type, which may be either the name of a
                            validation type or a specification for a
                            validation 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 subtype:
                                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 option's value
                     whenever it is changed by the object's configure or
                     configurelist methods.  In addition, all such options
                     will have their values validated automatically
                     immediately after the constructor executes.

                     Snit defines a family of validation types and subtypes,
                     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
                            -cgetmethod; 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
                            option 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
                            -configuremethod; 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
                            option 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
                            -validatemethod; it is called when the option's
                            value is set using the configure or configurelist
                            methods, just before the -configuremethod (if
                            any).  It is the named method's responsibility to
                            validate the option's new value, and to throw an
                            error if the value is invalid.

                            The named method must take two arguments, the
                            option name and its new value.  For example, this
                            code verifies that -flag's value is a valid
                            Boolean 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
                     arguments 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
                     constructor, 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 importing them,
              e.g., if the type name is ::parentns::typename, 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:
                     typically, the destruction of anything created in the
                     constructor.

                     The destructor takes no explicit arguments; 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.  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
                     ::parentns::typename, then the proc 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.

              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
                     component's command instead.  That is, the following
                     statement
                         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 delegated
              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
                            command.

                     %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
                            instance command; for Snit widgets and widget
                            adaptors, 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,
                     configurelist, or cget instance method is used to set or
                     retrieve 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
                     -configuremethod 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
                     automatically 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
                     mycomp 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 inherit, in a sense, the methods and
              options of the component. 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 delegated
              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
                            token, 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
              exceptions?
                     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
                     using 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 subcommands
              will be delegated to the tail type component.

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

                     If the -public option is specified, then the type
                     component is made public by defining a typemethod whose
                     subcommands are delegated to the type component, e.g.,
                     specifying -public mytypemethod is equivalent to the
                     following:
                         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
                     generates 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
                     -hasinstances 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
                            instance 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
                            documented 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
                            argument 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
                            dispatched normally.  If true, a faster
                            dispatching scheme is used instead.  The speed
                            comes at a price; with -simpledispatch yes you get
                            the following 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,
                                   configure, and configurelist) are very
                                   slightly slower.

              expose comp

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

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

                     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
                     requested widget name; then Snit does some magic,
                     renaming the hull component and installing its own
                     instance command 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
                     information.

              hulltype type
                     Determines the kind of widget used as the snit::widget's
                     hull.  The type may be frame (the default), toplevel,
                     labelframe; 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 lappend'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
              replaced 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::widgetadaptors 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
              instance 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
              statements in terms of the statements defined in this man page.

              A macro is simply a Tcl proc that is defined in the slave
              interpreter 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
              widgetadaptor, 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
              example, or run through the TclDevKit compiler.  In addition,
              the returned script could be saved in a ".tcl" file and used to
              define 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
              argument to the type command doesn't name a valid type method,
              unless 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
              -hastypemethods 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
              instance 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
              definition 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
              internal 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
              delegated type methods.

       $type info body method
              Returns the body of typemethod method. This method cannot be
              applied 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::widgets, 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
              options 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
              related 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
              includes local options and explicitly delegated options.  If
              unknown 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
              instances 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
              delegated, 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
              instance's method, in order. This method cannot be applied to
              delegated 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
              variable 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,
       destructors, 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
              commands to be passed to other objects.  It returns a command
              that when called will invoke type 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 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
              arguments, plus of course any arguments added by the caller.  In
              other words, both of the following commands will cause the
              object'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
              object, 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
              returned.  If option doesn't appear in the list, then the
              defvalue is returned.  If the option is locally-defined option,
              and defvalue is not specified, then the option's default value
              as specified 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
              Delegation.  Any additional args... are passed along with the
              name to the objType command.  If this is a snit::type, then the
              following 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 declared in
       the type definition using component, or must be referenced 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 information.

       install cannot be used to install type components; just assign the type
       component's command name to the type component's variable 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
              widget'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
              initializes 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::widgetadaptors 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
              namespaces 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
              automatically 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
              methods, 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
              object, 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
              object, 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
              command name, suitable for passing as a callback.

   COMPONENTS AND DELEGATION
       When an object includes other objects, as when a toolbar contains
       buttons or a GUI object contains an object that references a database,
       the included object is called a component.  The standard way to handle
       component objects owned by a Snit object is to declare them using
       component, 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
       widget'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
       specific 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
       interactions with the Tk option database; this is described in The Tk
       Option 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
       instance 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
       widget 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
              desired, set it explicitly using widgetclass in the widget
              definition.

       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::widgetadaptors.

       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
       unqualified 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::widget 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
       values by querying the Tk option database.  The resource name is
       usually just the option name minus the hyphen, but may contain
       uppercase letters 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
       inferred 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
       option 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
       -borderwidth, 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::widget 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 default; otherwise, the default hardcoded in the type
       definition is used.  In either case, the default can be overridden by
       the caller.  For example,

                  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
       implicitly 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
       delegated to the hull; thus, retrieving it is the same as retrieving
       -hullbackground.  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
       adaptors retain the widget class of their hull, and the hull is not
       created automatically by Snit.  Instead, the snit::widgetadaptor must
       call installhull 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
       command 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
       component 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
       create 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
       initialize 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
              inserting 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
              options implicitly delegated to the component that were not
              explicitly 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.
       However, 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
       following 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
       standard 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
       number 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
                     invalid if it is strictly less than min.

              -max max
                     Specifies a floating-point maximum bound; a value is
                     invalid 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
              following 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
                     integers.
                         option -numbers -type {snit::listtype -type snit::integer}

              Note that this option doesn't support defining new validation
              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-
                     sensitive.  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
              invalid.  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.
       Defining subtypes of Snit's validation types is described above, under
       Validation Types.

       The next simplest way to create a new validation type is as a
       validation 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 INVALID if the value is invalid.  This can be done with a
       simple proc.  For example, the snit::boolean validate type could have
       been implemented 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 at the
       SourceForge trackers for tcllib, which can be found at
       http://sourceforge.net/projects/tcllib/.  The relevant category is
       snit.

       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
       destruction 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 SourceForge Trackers at
              http://sourceforge.net/projects/tcllib/, category snit.

HISTORY
       During the course of developing Notebook (See
       http://www.wjduquette.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
       megawidgets easy.

       If you have any comments or suggestions (or bug reports!) don't
       hesitate 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
       William 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 SF Trackers
       [http://sourceforge.net/tracker/?group_id=12883].  Please also report
       any ideas for enhancements you may have for either package and/or
       documentation.

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

CATEGORY
       Programming tools

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




snit                                 2.3.2                             snit(n)
