NAME¶
scope - capture the namespace context for a variable
SYNOPSIS¶
itcl::scope name
DESCRIPTION¶
Creates a scoped value for the specified
name, which must be a variable
name. If the
name is an instance variable, then the scope command
returns a string of the following form:
This is recognized in any context as an instance variable belonging to
object. So with itcl3.0 and beyond, it is possible to use instance
variables in conjunction with widgets. For example, if you have an object with
a private variable x, and you can use x in conjunction with the -textvariable
option of an entry widget. Before itcl3.0, only common variables could be used
in this manner.
If the
name is not an instance variable, then it must be a common
variable or a global variable. In that case, the scope command returns the
fully qualified name of the variable, e.g., ::foo::bar::x.
If the
name is not recognized as a variable, the scope command returns an
error.
Ordinary variable names refer to variables in the global namespace. A scoped
value captures a variable name together with its namespace context in a way
that allows it to be referenced properly later. It is needed, for example, to
wrap up variable names when a Tk widget is used within a namespace:
namespace foo {
private variable mode 1
radiobutton .rb1 -text "Mode #1" -variable [scope mode] -value 1
pack .rb1
radiobutton .rb2 -text "Mode #2" -variable [scope mode] -value 2
pack .rb2
}
Radiobuttons .rb1 and .rb2 interact via the variable "mode" contained
in the namespace "foo". The
scope command guarantees this by
returning the fully qualified variable name ::foo::mode.
You should never use the @itcl syntax directly. For example, it is a bad idea to
write code like this:
set {@itcl ::fred x} 3
puts "value = ${@itcl ::fred x}"
Instead, you should always use the scope command to generate the variable name
dynamically. Then, you can pass that name to a widget or to any other bit of
code in your program.
KEYWORDS¶
code, namespace, variable