trusty (3) code.3itcl.gz

NAME

       code - capture the namespace context for a code fragment

SYNOPSIS

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

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  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!"]  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