NAME¶
Sub::Uplevel - apparently run a function in a higher stack frame
VERSION¶
version 0.24
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
http://rt.cpan.org/Public/Dist/Display.html?Name=Sub-Uplevel
<
http://rt.cpan.org/Public/Dist/Display.html?Name=Sub-Uplevel>. 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/dagolden/sub-uplevel
<
https://github.com/dagolden/sub-uplevel>
git clone https://github.com/dagolden/sub-uplevel.git
AUTHORS¶
- •
- Michael Schwern <mschwern@cpan.org>
- •
- David Golden <dagolden@cpan.org>
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2012 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.