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