libsub-uplevel-perl/README

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.