itclvars(n) [incr Tcl] itclvars(n) ______________________________________________________________________________
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 "back-
ward-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-qual-
ified 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 encapsu-
lation, 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
itcl 3.0 itclvars(n)
tcl 8.6.9 - Generated Fri Nov 16 19:12:02 CST 2018