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.