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'\" RCS: $Id: code.n,v 1.1.1.1 2002-01-16 10:24:46 markom Exp $

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.so man.macros

.TH code n 3.0 itcl "[incr\ Tcl]"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

code \- capture the namespace context for a code fragment

.SH SYNOPSIS

\fBcode \fR?\fB-namespace \fIname\fR? \fIcommand \fR?\fIarg arg ...\fR?

.BE

.SH DESCRIPTION

.PP

Creates a scoped value for the specified \fIcommand\fR and its

associated \fIarg\fR arguments.  A scoped value is a list with three

elements:  the "\fC@scope\fR" keyword, a namespace context,

and a value string.  For example, the command

.CS

namespace foo {

    code puts "Hello World!"

}

.CE

produces the scoped value:

.CS

@scope ::foo {puts {Hello World!}}

.CE

Note that the \fBcode\fR command captures the current namespace

context.  If the \fB-namespace\fR flag is specified, then the

current context is ignored, and the \fIname\fR string is used

as the namespace context.

.PP

Extensions like Tk execute ordinary code fragments in the global

namespace.  A scoped value captures a code fragment together with

its namespace context in a way that allows it to be executed

properly later.  It is needed, for example, to wrap up code fragments

when a Tk widget is used within a namespace:

.CS

namespace foo {

    private proc report {mesg} {

        puts "click: $mesg"

    }

    button .b1 -text "Push Me" \

        -command [code report "Hello World!"]

    pack .b1

}

.CE

The code fragment associated with button \fC.b1\fR only makes

sense in the context of namespace "foo".  Furthermore, the

"report" procedure is private, and can only be accessed within

that namespace.  The \fBcode\fR command wraps up the code

fragment in a way that allows it to be executed properly

when the button is pressed.

.PP

Also, note that the \fBcode\fR command preserves the integrity

of arguments on the command line.  This makes it a natural replacement

for the \fBlist\fR command, which is often used to format Tcl code

fragments.  In other words, instead of using the \fBlist\fR command

like this:

.CS

after 1000 [list puts "Hello $name!"]

.CE

use the \fBcode\fR command like this:

.CS

after 1000 [code puts "Hello $name!"]

.CE

This not only formats the command correctly, but also captures

its namespace context.

.PP

Scoped commands can be invoked like ordinary code fragments, with

or without the \fBeval\fR command.  For example, the following

statements work properly:

.CS

set cmd {@scope ::foo .b1}

$cmd configure -background red

set opts {-bg blue -fg white}

eval $cmd configure $opts

.CE

Note that scoped commands by-pass the usual protection mechanisms;

the command:

.CS

@scope ::foo {report {Hello World!}}

.CE

can be used to access the "foo::report" proc from any namespace

context, even though it is private.

.SH KEYWORDS

scope, callback, namespace, public, protected, private