itcl::option - define options for extendedclass, widget or widgetadaptor

       The option command is used inside an [incrTcl] extendedclass/widget/widgetadaptor definition  to  define
       options.

       In the first form 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 optionSpec 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 $itcl_options(-font)

       In the second form you can define 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:

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

       -readonly
              The  option  is handled read-only -- it can only be set using configure at creation time, i.e., in
              the type's constructor.

       -cgetmethodmethodName
              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) Itcl's default handling of cget:

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

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

       -cgetmethodvarvarName
              That  is  very similar to -cgetmethod, the only difference is, one can define a variable, where to
              find the cgetmethod during runtime.

       -configuremethodmethodName
              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  itcl_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) Itcl's default handling of configure:

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

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

       -configuremethodvarvarName
              That is very similar to -configuremethod, the only difference is, one can define a variable, where
              to find the configuremethod during runtime.

       -validatemethodmethodName
              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.

       -validatemethodvarvarName
              That  is very similar to -validatemethod, the only difference is, one can define a variable, where
              to find the validatemethod during runtime.

       option, widget, widgetadaptor, extendedclass

itcl                                                   4.0                                         option(3itcl)

       itcl::option - define options for extendedclass, widget or widgetadaptor

       Parts  of  this  description  are  "borrowed"  from  Tcl extension [snit], as the functionality is mostly
       identical.

optionoptionSpec ?defaultValue?
       optionoptionSpec ?options?
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       This is new functionality in [incr Tcl] where the API can still change!!