Sub::Uplevel - apparently run a function in a higher stack frame
version 0.2800
use Sub::Uplevel;
sub foo {
print join " - ", caller;
}
sub bar {
uplevel 1, \&foo;
}
#line 11
bar(); # main - foo.plx - 11
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.
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.
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.
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 to Brent Welch, Damian Conway and Robin Houston.
See http://www.perl.com/perl/misc/Artistic.html
PadWalker (for the similar idea with lexicals), Hook::LexWrap,
Tcl's uplevel() at http://www.scriptics.com/man/tcl8.4/TclCmd/uplevel.htm
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.
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
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.
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