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 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;
    }

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

Symbol::Uplevel must be used as early as possible in your program's compilation.

Well, the bad news is uplevel() is about 5 times slower than a normal function call. XS implementation anyone?

Blows over any CORE::GLOBAL::caller you might have (and if you do, you're just sick). Will be fixed in a newer version.

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.

AUTHOR

Michael G Schwern <schwern@pobox.com>

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