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?

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.

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