Sub::Uplevel

Sub::Uplevel(3)	     User Contributed Perl Documentation      Sub::Uplevel(3)



NAME
       Sub::Uplevel - apparently run a function in a higher stack frame

SYNOPSIS
	 use Sub::Uplevel;

	 sub foo {
	     print join " - ", caller;
	 }

	 sub bar {
	     uplevel 1, \&foo;
	 }

	 #line 11
	 bar();	   # main - foo.plx - 11

DESCRIPTION
       Like Tcl’s uplevel() function, but not quite so dangerous.  The idea
       is just to fool caller().  All the really naughty bits of Tcl’s
       uplevel() are avoided.

       THIS IS NOT THE SORT OF THING YOU WANT TO DO EVERYDAY

       uplevel
	     uplevel $num_frames, \&func, @args;

	   Makes the given function think it’s being executed $num_frames
	   higher than the current stack level.	 So when they use
	   caller($frames) it will actually give caller($frames +
	   $num_frames) for them.

	   "uplevel(1, \&some_func, @_)" is effectively "goto &some_func" but
	   you don’t immediately exit the current subroutine.  So while you
	   can’t do this:

	       sub wrapper {
		   print "Before\n";
		   goto &some_func;
		   print "After\n";
	       }

	   you can do this:

	       sub wrapper {
		   print "Before\n";
		   my @out = uplevel 1, &some_func;
		   print "After\n";
		   return @out;
	       }

EXAMPLE
       The main reason I wrote this module is so I could write wrappers
       around functions and they wouldn’t be aware they’ve been wrapped.

	   use Sub::Uplevel;

	   my $original_foo = \&foo;

	   *foo = sub {
	       my @output = uplevel 1, $original_foo;
	       print "foo() returned:  @output";
	       return @output;
	   };

       If this code frightens you you should not use this module.

BUGS and CAVEATS
       Well, the bad news is uplevel() is about 5 times slower than a normal
       function call.  XS implementation anyone?

       Sub::Uplevel overrides CORE::GLOBAL::caller temporarily for the scope
       of each uplevel call.  It does its best to work with any previously
       existing CORE::GLOBAL::caller (both when Sub::Uplevel is first loaded
       and within each uplevel call) such as from Contextual::Return or
       Hook::LexWrap.

       However, if you are routinely using multiple modules that override
       CORE::GLOBAL::caller, you are probably asking for trouble.

HISTORY
       Those who do not learn from HISTORY are doomed to repeat it.

       The lesson here is simple:  Don’t sit next to a Tcl programmer at the
       dinner table.

THANKS
       Thanks to Brent Welch, Damian Conway and Robin Houston.

AUTHORS
       David A Golden <dagolden@cpan.org> (current maintainer)

       Michael G Schwern <schwern@pobox.com> (original author)

LICENSE
       Original code Copyright (c) 2001 to 2007 by Michael G Schwern.  Addi-
       tional code Copyright (c) 2006 to 2007 by David A Golden.

       This program is free software; you can redistribute it and/or modify
       it under the same terms as Perl itself.

       See http://www.perl.com/perl/misc/Artistic.html

SEE ALSO
       PadWalker (for the similar idea with lexicals), Hook::LexWrap, Tcl’s
       uplevel() at http://www.scriptics.com/man/tcl8.4/TclCmd/uplevel.htm



perl v5.8.8			  2007-07-30		      Sub::Uplevel(3)