code(n) [incr Tcl] code(n) ______________________________________________________________________________
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 names-
pace. A scoped value captures a code fragment together with its names-
pace 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 com-
mand 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 con-
text, even though it is private.
KEYWORDS
scope, callback, namespace, public, protected, private
itcl 3.0 code(n)
Mac OS X 10.8 - Generated Wed Sep 5 16:11:29 CDT 2012