NAME
code - capture the namespace context for a code fragment
SYNOPSIS
code ?-namespace name? command ?arg arg ...?
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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 con
text, 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 exam
ple, 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!"]
tures its namespace context.
Scoped commands can be invoked like ordinary code frag
ments, 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
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