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'\"
'\" Copyright (c) 1993-1998 Lucent Technologies, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH scope n "" itcl "[incr\ Tcl]"
.so man.macros
.BS
'\" Note: do not modify the .SH NAME line immediately below!
.SH NAME
itcl::scope \- capture the namespace context for a variable
.SH SYNOPSIS
\fBitcl::scope \fIname\fR
.BE
.SH DESCRIPTION
.PP
Creates a scoped value for the specified \fIname\fR, which must
be a variable name. If the \fIname\fR is an instance variable,
then the scope command returns a name which will resolve in any
context as an instance variable belonging to \fIobject\fR.
The precise format of this name is an internal detail to Itcl.
Use of such a scoped value makes it possible to use
instance variables in conjunction with widgets. For example, if you
have an object with a private variable \fCx\fR, and you can use
\fCx\fR in conjunction with the \fC-textvariable\fR option of an
entry widget. Before itcl3.0, only common variables could be used
in this manner.
.PP
If the \fIname\fR is not an instance variable, then it must be
a common variable or a global variable. In that case, the scope
command returns the fully qualified name of the variable, e.g.,
\fC::foo::bar::x\fR.
.PP
If the \fIname\fR is not recognized as a variable, the scope
command returns an error.
.PP
Ordinary variable names refer to variables in the global namespace.
A scoped value captures a variable name together with its namespace
context in a way that allows it to be referenced properly later.
It is needed, for example, to wrap up variable names when a Tk
widget is used within a namespace:
.CS
namespace foo {
private variable mode 1
radiobutton .rb1 -text "Mode #1" \
-variable [scope mode] -value 1
pack .rb1
radiobutton .rb2 -text "Mode #2" \
-variable [scope mode] -value 2
pack .rb2
}
.CE
Radiobuttons \fC.rb1\fR and \fC.rb2\fR interact via the variable
"mode" contained in the namespace "foo". The \fBscope\fR command
guarantees this by returning the fully qualified variable name
\fC::foo::mode\fR.
.PP
You should never attempt to craft your own scoped variable names,
even if you believe you've flawlessly reverse-engineered the encoding.
Instead, you should always use the scope command to generate the
variable name dynamically. Then, you can pass that name to a widget
or to any other bit of code in your program.
.SH KEYWORDS
code, namespace, variable
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