bionic (3) itclvars.3itcl.gz

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.

       itcl::library
              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.

       itcl::patchLevel
              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.

       itcl::purist
              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.

       itcl::version
              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