DOKK / manpages / debian 10 / tcl-itcl4-doc / itcloption.3itcl.en
option(3itcl) [incr Tcl] 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.








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








option optionSpec ?defaultValue?
option optionSpec ?options?












The option command is used inside an
    [incr Tcl] 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:



  

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

  

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

  

  
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.





  

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

  

  
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.





  

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

  

  
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.





  

  
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







  

    4.0
    itcl