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] initial
izes 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] initial
izes 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 vari
able controls a "backward-compatibility" mode for
widget access.
In vanilla Tcl/Tk, there is a single pool of com
mands, 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 conjunc
tion 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.
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-compatibil
ity mode. By default, this variable is "0", and the win
dow 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] initial
izes 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
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