1scope(n)                          [incr Tcl]                          scope(n)
2
3
4
5______________________________________________________________________________
6

NAME

8       itcl::scope - capture the namespace context for a variable
9

SYNOPSIS

11       itcl::scope name
12______________________________________________________________________________
13
14

DESCRIPTION

16       Creates a scoped value for the specified name, which must be a variable
17       name.  If the name is an instance  variable,  then  the  scope  command
18       returns a string of the following form:
19              @itcl object varName
20       This  is recognized in any context as an instance variable belonging to
21       object.  So with itcl3.0 and beyond, it is  possible  to  use  instance
22       variables  in  conjunction  with  widgets.  For example, if you have an
23       object with a private variable x, and you can use x in conjunction with
24       the -textvariable option of an entry widget.  Before itcl3.0, only com‐
25       mon variables could be used in this manner.
26
27       If the name is not an instance variable, then it must be a common vari‐
28       able or a global variable.  In that case, the scope command returns the
29       fully qualified name of the variable, e.g., ::foo::bar::x.
30
31       If the name is not recognized as a variable, the scope command  returns
32       an error.
33
34       Ordinary  variable names refer to variables in the global namespace.  A
35       scoped value captures a variable name together with its namespace  con‐
36       text  in  a  way that allows it to be referenced properly later.  It is
37       needed, for example, to wrap up variable names when a Tk widget is used
38       within a namespace:
39              namespace foo {
40                  private variable mode 1
41
42                  radiobutton .rb1 -text "Mode #1"         -variable [scope mode] -value 1
43                  pack .rb1
44
45                  radiobutton .rb2 -text "Mode #2"         -variable [scope mode] -value 2
46                  pack .rb2
47              }
48       Radiobuttons  .rb1  and .rb2 interact via the variable "mode" contained
49       in the namespace "foo".  The scope command guarantees this by returning
50       the fully qualified variable name ::foo::mode.
51
52       You  should  never use the @itcl syntax directly.  For example, it is a
53       bad idea to write code like this:
54              set {@itcl ::fred x} 3
55              puts "value = ${@itcl ::fred x}"
56       Instead, you should always use the scope command to generate the  vari‐
57       able  name dynamically.  Then, you can pass that name to a widget or to
58       any other bit of code in your program.
59
60

KEYWORDS

62       code, namespace, variable
63
64
65
66itcl                                                                  scope(n)