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ActiveTcl 8.5 documentation
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ActiveTcl User Guide |
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[incr\ Tcl]
NAME
code - capture the namespace context for a code fragment
SYNOPSIS
itcl::code ?-namespace name? command
?arg arg ...?
DESCRIPTION
Creates a scoped value for the specified command and its
associated arg arguments. A scoped value is a list with
three elements: the "@scope" keyword, a namespace context, and a
value string. For example, the command
namespace foo {
code puts "Hello World!"
}
produces the scoped value:
@scope ::foo {puts {Hello World!}}
Note that the code command captures the current namespace
context. If the -namespace flag is specified, then the
current context is ignored, and the name string is used as
the namespace context.
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:
namespace foo {
private proc report {mesg} {
puts "click: $mesg"
}
button .b1 -text "Push Me"
-command [code report "Hello World!"]
pack .b1
}
The code fragment associated with button .b1 only makes sense in
the context of namespace "foo". Furthermore, the "report" procedure
is private, and can only be accessed within that namespace. The
code command wraps up the code fragment in a way that allows
it to be executed properly when the button is pressed.
Also, note that the code command preserves the integrity
of arguments on the command line. This makes it a natural
replacement for the list command, which is often used to
format Tcl code fragments. In other words, instead of using the
list command like this:
after 1000 [list puts "Hello $name!"]
use the code command like this:
after 1000 [code puts "Hello $name!"]
This not only formats the command correctly, but also captures its
namespace context.
Scoped commands can be invoked like ordinary code fragments,
with or without the eval command. For example, the following
statements work properly:
set cmd {@scope ::foo .b1}
$cmd configure -background red
set opts {-bg blue -fg white}
eval $cmd configure $opts
Note that scoped commands by-pass the usual protection mechanisms;
the command:
@scope ::foo {report {Hello World!}}
can be used to access the "foo::report" proc from any namespace
context, even though it is private.
KEYWORDS
scope, callback, namespace, public, protected, private
[ itcl ]
Copyright © 1989-1994 The Regents of the University of California.
Copyright © 1994-1996 Sun Microsystems, Inc.
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