Sub::Uplevel(3pm) - phpMan

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



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 immedi-
           ately 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 Contex-
       tual::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 AT cpan.org> (current maintainer)

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

LICENSE
       Original code Copyright (c) 2001 to 2007 by Michael G Schwern.  Additional code Copyright
       (c) 2006 to 2008 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                                 2008-02-17                          Sub::Uplevel(3pm)

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