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code(3itcl) [incr Tcl] code(3itcl) 





NAME


itcl::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







  

    3.0
    itcl