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itclvars(3itcl) [incr Tcl] itclvars(3itcl) 





NAME


itclvars - variables used by [incr Tcl]










DESCRIPTION


The following global variables are created and managed
    automatically by the [incr Tcl] library. Except where noted
    below, these variables should normally be treated as read-only by
    application-specific code and by users.



  

  
When an interpreter is created, [incr Tcl] initializes this
      variable to hold the name of a directory containing the system library of
      [incr Tcl] scripts. The initial value of
      itcl::library is set from the ITCL_LIBRARY environment variable if
      it exists, or from a compiled-in value otherwise.

  

  
When an interpreter is created, [incr Tcl] initializes this
      variable to hold the current patch level for [incr Tcl]. For
      example, the value "2.0p1" indicates
      [incr Tcl] version 2.0 with the first set of patches
      applied.

  

  
When an interpreter is created containing Tcl/Tk and the
      [incr Tcl] namespace facility, this variable controls a
      "backward-compatibility" mode for widget access.
    
In vanilla Tcl/Tk, there is a single pool of commands, so the
        access command for a widget is the same as the window name. When a
        widget is created within a namespace, however, its access command is
        installed in that namespace, and should be accessed outside of the
        namespace using a qualified name. For example,

  






namespace foo {


    namespace bar {


        button .b -text "Testing"


    }
}
foo::bar::.b configure -background red
pack .b



Note that the window name ".b" is still used in conjunction with
  commands like pack and destroy. However, the access command for
  the widget (i.e., name that appears as the first argument on a command
  line) must be more specific.

The "winfo command" command can be used to query
    the fully-qualified access command for any widget, so one can write:




[winfo command .b] configure -background red



and this is good practice when writing library procedures. Also, in conjunction
  with the bind command, the "%q" field can be used in place of
  "%W" as the access command:



bind Button <Key-Return> {%q flash; %q invoke}



While this behavior makes sense from the standpoint of encapsulation, it causes
  problems with existing Tcl/Tk applications. Many existing applications are
  written with bindings that use "%W". Many library procedures assume
  that the window name is the access command.

The itcl::purist variable controls a backward-compatibility
    mode. By default, this variable is "0", and the window name can be
    used as an access command in any context. Whenever the unknown
    procedure stumbles across a widget name, it simply uses "winfo
    command" to determine the appropriate command name. If this
    variable is set to "1", this backward-compatibility mode is
    disabled. This gives better encapsulation, but using the window name as the
    access command may lead to "invalid command" errors.



  

  
When an interpreter is created, [incr Tcl] initializes this
      variable to hold the version number of the form x.y. Changes to
      x represent major changes with probable incompatibilities and
      changes to y represent small enhancements and bug fixes that retain
      backward compatibility.
    

  








KEYWORDS


itcl, variables







  

    3.0
    itcl