Sub::Uplevel--3pm

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 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
       Sub::Uplevel must be used as early as possible in your program's compi-
       lation.

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

       Blows over any CORE::GLOBAL::caller you might have (and if you do,
       you're just sick).

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
       Copyright by Michael G Schwern, 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                       2006-11-06                 Sub::Uplevel(3pm)