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



NAME
       code - capture the namespace context for a code fragment

SYNOPSIS
       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  cur-
       rent  context  is ignored, and the name string is used as the namespace
       context.

       Extensions like Tk execute ordinary code fragments in the global names-
       pace.  A scoped value captures a code fragment together with its names-
       pace 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  pri-
       vate.


KEYWORDS
       scope, callback, namespace, public, protected, private



itcl                                  3.0                              code(n)