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scope(3itcl) [incr Tcl] scope(3itcl) 





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:




@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 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







  

    
    itcl