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-spe-cific application-specific
cific 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 com-piled-in compiled-in
piled-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 spe-cific. specific.
cific.
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 prac-tice practice
tice 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 bind-ings bindings
ings that use "%W". Many library procedures assume that the window name is the access com-mand. command.
mand.
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 num-ber number
ber 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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