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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;
               }

           "uplevel" will issue a warning if $num_frames is more than the current call stack depth.

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?  It also slows down every invocation of caller(), regardless of whether
       uplevel() is in effect.

       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.

       You should load Sub::Uplevel as early as possible within your program.  As with all CORE::GLOBAL
       overloading, the overload will not affect modules that have already been compiled prior to the
       overload.  One module that often is unavoidably loaded prior to Sub::Uplevel is Exporter.  To
       forceably recompile Exporter (and Exporter::Heavy) after loading Sub::Uplevel, use it with the
       ":aggressive" tag:

           use Sub::Uplevel qw/:aggressive/;

       The private function "Sub::Uplevel::_force_reload()" may be passed a list of additional modules to
       reload if ":aggressive" is not aggressive enough.  Reloading modules may break things, so only use
       this as a last resort.

       As of version 0.20, Sub::Uplevel requires Perl 5.6 or greater.

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.  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 v5.12.5                                     2013-08-25                                  Sub::Uplevel(3)