NAME

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

VERSION

       version 0.2800

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" has the ability to issue a warning if $num_frames is more than the current
           call stack depth, although this warning is disabled and compiled out by default as the
           check is relatively expensive.

           To enable the check for debugging or testing, you should set the global
           $Sub::Uplevel::CHECK_FRAMES to true before loading Sub::Uplevel for the first time as
           follows:

               #!/usr/bin/perl

               BEGIN {
                   $Sub::Uplevel::CHECK_FRAMES = 1;
               }
               use Sub::Uplevel;

           Setting or changing the global after the module has been loaded will have no effect.

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 forcibly 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.

       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

SUPPORT

   Bugs / Feature Requests
       Please report any bugs or feature requests through the issue tracker at
       <https://github.com/Perl-Toolchain-Gang/Sub-Uplevel/issues>.  You will be notified
       automatically of any progress on your issue.

   Source Code
       This is open source software.  The code repository is available for public review and
       contribution under the terms of the license.

       <https://github.com/Perl-Toolchain-Gang/Sub-Uplevel>

         git clone https://github.com/Perl-Toolchain-Gang/Sub-Uplevel.git

AUTHORS

       •   Michael Schwern <mschwern@cpan.org>

       •   David Golden <dagolden@cpan.org>

CONTRIBUTORS

       •   Adam Kennedy <adamk@cpan.org>

       •   Alexandr Ciornii <alexchorny@gmail.com>

       •   David Golden <xdg@xdg.me>

       •   Graham Ollis <plicease@cpan.org>

       •   J. Nick Koston <nick@cpanel.net>

       •   Michael Gray <mg13@sanger.ac.uk>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2017 by Michael Schwern and David Golden.

       This is free software; you can redistribute it and/or modify it under the same terms as
       the Perl 5 programming language system itself.