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 ITCLIBRARY 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 "2.00p1" 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 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-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 {%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)
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