itcloption man page on Archlinux

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option(n)			  [incr Tcl]			     option(n)

______________________________________________________________________________

NAME
       itcl::option  - define options for extendedclass, widget or widgetadap‐
       tor

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

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

SYNOPSIS
       option optionSpec ?defaultValue?
       option optionSpec ?options?
_________________________________________________________________

DESCRIPTION
       The option command is  used  inside  an	[incr Tcl]  extendedclass/wid‐
       get/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., -config‐
       uremethod), then it should probably use configure and  cget  to	access
       its options to avoid subtle errors.

       The option statement may include the following options:

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

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

       -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) 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.

       -cgetmethodvar varName
	      That is very similar to -cgetmethod, the only difference is, one
	      can define a variable, where to find the cgetmethod during  run‐
	      time.

       -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 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.

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

       -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.

       -validatemethodvar varName
	      That is very similar to -validatemethod, the only difference is,
	      one can define a variable, where to find the validatemethod dur‐
	      ing runtime.

KEYWORDS
       option, widget, widgetadaptor, extendedclass

itcl				      4.0			     option(n)
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