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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


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(3), 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

       o   Michael Schwern <mschwern@cpan.org>

       o   David Golden <dagolden@cpan.org>


CONTRIBUTORS

       o   Adam Kennedy <adamk@cpan.org>

       o   Alexandr Ciornii <alexchorny@gmail.com>

       o   David Golden <xdg@xdg.me>

       o   Graham Ollis <plicease@cpan.org>

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

       o   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.



perl v5.34.1                       2017-04-01                    Sub::Uplevel(3)

sub-uplevel 0.280.0 - Generated Fri Apr 28 07:46:10 CDT 2023
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