scope(n) [incr Tcl] scope(n)______________________________________________________________________________NAME
itcl::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:
@itcl object varName
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 com‐
mon variables could be used in this manner.
If the name is not an instance variable, then it must be a common vari‐
able 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 con‐
text 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 vari‐
able 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
itclscope(n)
