NAME

       code - capture the namespace context for a code fragment


SYNOPSIS

       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 con­
       text, 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 exam­
       ple,  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  executed  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!"]

       tures its namespace context.

       Scoped commands can be invoked like  ordinary  code  frag­
       ments, 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


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