bionic (3) scope.3itcl.gz

NAME

       scope - capture the namespace context for a variable

SYNOPSIS

       itcl::scope name
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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