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markom |
'\"
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'\" Copyright (c) 1993-1998 Lucent Technologies, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" RCS: $Id: scope.n,v 1.1.1.1 2002-01-16 10:24:46 markom Exp $
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'\"
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.so man.macros
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.TH scope n "" Tcl "[incr\ Tcl]"
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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scope \- capture the namespace context for a variable
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.SH SYNOPSIS
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\fBscope \fIname\fR
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.BE
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.SH DESCRIPTION
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.PP
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Creates a scoped value for the specified \fIname\fR, which must
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be a variable name. If the \fIname\fR is an instance variable,
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then the scope command returns a string of the following form:
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.CS
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@itcl \fIobject varName\fP
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.CE
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This is recognized in any context as an instance variable belonging
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to \fIobject\fR. So with itcl3.0 and beyond, it is possible to use
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instance variables in conjunction with widgets. For example, if you
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have an object with a private variable \fCx\fR, and you can use
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\fCx\fR in conjunction with the \fC-textvariable\fR option of an
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entry widget. Before itcl3.0, only common variables could be used
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in this manner.
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.PP
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If the \fIname\fR is not an instance variable, then it must be
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a common variable or a global variable. In that case, the scope
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command returns the fully qualified name of the variable, e.g.,
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\fC::foo::bar::x\fR.
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.PP
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If the \fIname\fR is not recognized as a variable, the scope
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command returns an error.
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.PP
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Ordinary variable names refer to variables in the global namespace.
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A scoped value captures a variable name together with its namespace
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context in a way that allows it to be referenced properly later.
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It is needed, for example, to wrap up variable names when a Tk
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widget is used within a namespace:
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.CS
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namespace foo {
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private variable mode 1
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radiobutton .rb1 -text "Mode #1" \
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-variable [scope mode] -value 1
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pack .rb1
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radiobutton .rb2 -text "Mode #2" \
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-variable [scope mode] -value 2
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pack .rb2
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}
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.CE
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Radiobuttons \fC.rb1\fR and \fC.rb2\fR interact via the variable
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"mode" contained in the namespace "foo". The \fBscope\fR command
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guarantees this by returning the fully qualified variable name
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\fC::foo::mode\fR.
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.PP
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You should never use the \fC@itcl\fR syntax directly. For example,
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it is a bad idea to write code like this:
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.CS
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set {@itcl ::fred x} 3
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puts "value = ${@itcl ::fred x}"
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.CE
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Instead, you should always use the scope command to generate the
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variable name dynamically. Then, you can pass that name to a widget
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or to any other bit of code in your program.
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.SH KEYWORDS
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code, namespace, variable
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