itclvars(n) [incr Tcl] itclvars(n)
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NAME
itclvars - variables used by [incr Tcl]
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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-compati-
bility" 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 wid-
get (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 encapsula-
tion, 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 rep-
resent major changes with probable incompatibilities and changes to y represent small enhancements and bug fixes that retain back-
ward compatibility.
KEYWORDS
itcl, variables
itcl 3.0 itclvars(n)