code man page on Archlinux

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


       itcl::code - capture the namespace context for a code fragment

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

       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
	      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 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 com‐
       mand  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
	      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
	      @scope ::foo {report {Hello World!}}
       can  be	used  to access the "foo::report" proc from any namespace con‐
       text, even though it is private.

       scope, callback, namespace, public, protected, private

itcl				      3.0			       code(n)

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