code(n)                                                             [incr Tcl]                                                             code(n)

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NAME

       code - capture the namespace context for a code fragment

SYNOPSIS

       itcl::code ?-namespace name? command ?arg arg ...?
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DESCRIPTION

       Creates  a  scoped  value  for  the specified command and its associated arg arguments.  A scoped value is a list with three elements:  the
       "@scope" keyword, a namespace context, and a value string.  For example, the command
              namespace foo {
                  code puts "Hello World!"
              }
       produces the scoped value:
              @scope ::foo {puts {Hello World!}}
       Note that the code command captures the current namespace context.  If the -namespace flag  is  specified,  then  the  current  context  is
       ignored, and the name string is used as the namespace context.

       Extensions  like  Tk  execute  ordinary  code fragments in the global namespace.  A scoped value captures a code fragment together with its
       namespace context in a way that allows it to be executed properly later.  It is needed, for example, to wrap up code fragments  when  a  Tk
       widget is used within a namespace:
              namespace foo {
                  private proc report {mesg} {
                      puts "click: $mesg"
                  }

                  button .b1 -text "Push Me"         -command [code report "Hello World!"]
                  pack .b1
              }
       The  code  fragment  associated with button .b1 only makes sense in the context of namespace "foo".  Furthermore, the "report" procedure is
       private, and can only be accessed within that namespace.  The code command wraps up the code fragment in a way that allows it  to  be  exe-
       cuted properly when the button is pressed.

       Also,  note  that  the  code command preserves the integrity of arguments on the command line.  This makes it a natural replacement for the
       list command, which is often used to format Tcl code fragments.  In other words, instead of using the list command like this:
              after 1000 [list puts "Hello $name!"]
       use the code command like this:
              after 1000 [code puts "Hello $name!"]
       This not only formats the command correctly, but also captures its namespace context.

       Scoped commands can be invoked like ordinary code fragments, with or without the eval command.  For example, the following statements  work
       properly:
              set cmd {@scope ::foo .b1}
              $cmd configure -background red

              set opts {-bg blue -fg white}
              eval $cmd configure $opts
       Note that scoped commands by-pass the usual protection mechanisms; the command:
              @scope ::foo {report {Hello World!}}
       can be used to access the "foo::report" proc from any namespace context, even though it is private.

KEYWORDS

       scope, callback, namespace, public, protected, private

itcl                                                                    3.0                                                                code(n)