File: //usr/local/ssl/local/share/man/man3/Sub::Uplevel.3
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.\" ========================================================================
.\"
.IX Title "Sub::Uplevel 3"
.TH Sub::Uplevel 3 "2009-11-17" "perl v5.8.8" "User Contributed Perl Documentation"
.SH "NAME"
Sub::Uplevel \- apparently run a function in a higher stack frame
.SH "VERSION"
.IX Header "VERSION"
This documentation describes version 0.22
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& use Sub::Uplevel;
.Ve
.PP
.Vb 3
\& sub foo {
\& print join " - ", caller;
\& }
.Ve
.PP
.Vb 3
\& sub bar {
\& uplevel 1, \e&foo;
\& }
.Ve
.PP
.Vb 2
\& #line 11
\& bar(); # main - foo.plx - 11
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Like Tcl's \fIuplevel()\fR function, but not quite so dangerous. The idea
is just to fool \fIcaller()\fR. All the really naughty bits of Tcl's
\&\fIuplevel()\fR are avoided.
.PP
\&\fB\s-1THIS\s0 \s-1IS\s0 \s-1NOT\s0 \s-1THE\s0 \s-1SORT\s0 \s-1OF\s0 \s-1THING\s0 \s-1YOU\s0 \s-1WANT\s0 \s-1TO\s0 \s-1DO\s0 \s-1EVERYDAY\s0\fR
.IP "\fBuplevel\fR" 4
.IX Item "uplevel"
.Vb 1
\& uplevel $num_frames, \e&func, @args;
.Ve
.Sp
Makes the given function think it's being executed \f(CW$num_frames\fR higher
than the current stack level. So when they use caller($frames) it
will actually give caller($frames + \f(CW$num_frames\fR) for them.
.Sp
\&\f(CW\*(C`uplevel(1, \e&some_func, @_)\*(C'\fR is effectively \f(CW\*(C`goto &some_func\*(C'\fR but
you don't immediately exit the current subroutine. So while you can't
do this:
.Sp
.Vb 5
\& sub wrapper {
\& print "Before\en";
\& goto &some_func;
\& print "After\en";
\& }
.Ve
.Sp
you can do this:
.Sp
.Vb 6
\& sub wrapper {
\& print "Before\en";
\& my @out = uplevel 1, &some_func;
\& print "After\en";
\& return @out;
\& }
.Ve
.Sp
\&\f(CW\*(C`uplevel\*(C'\fR will issue a warning if \f(CW$num_frames\fR is more than the current call
stack depth.
.SH "EXAMPLE"
.IX Header "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.
.PP
.Vb 1
\& use Sub::Uplevel;
.Ve
.PP
.Vb 1
\& my $original_foo = \e&foo;
.Ve
.PP
.Vb 5
\& *foo = sub {
\& my @output = uplevel 1, $original_foo;
\& print "foo() returned: @output";
\& return @output;
\& };
.Ve
.PP
If this code frightens you \fByou should not use this module.\fR
.SH "BUGS and CAVEATS"
.IX Header "BUGS and CAVEATS"
Well, the bad news is \fIuplevel()\fR is about 5 times slower than a normal
function call. \s-1XS\s0 implementation anyone? It also slows down every invocation
of \fIcaller()\fR, regardless of whether \fIuplevel()\fR is in effect.
.PP
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.
.PP
However, if you are routinely using multiple modules that override
CORE::GLOBAL::caller, you are probably asking for trouble.
.PP
You \fBshould\fR load Sub::Uplevel as early as possible within your program. As
with all \s-1CORE::GLOBAL\s0 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 forceably recompile
Exporter (and Exporter::Heavy) after loading Sub::Uplevel, use it with the
\&\*(L":aggressive\*(R" tag:
.PP
.Vb 1
\& use Sub::Uplevel qw/:aggressive/;
.Ve
.PP
The private function \f(CW\*(C`Sub::Uplevel::_force_reload()\*(C'\fR may be passed a list of
additional modules to reload if \*(L":aggressive\*(R" is not aggressive enough.
Reloading modules may break things, so only use this as a last resort.
.PP
As of version 0.20, Sub::Uplevel requires Perl 5.6 or greater.
.SH "HISTORY"
.IX Header "HISTORY"
Those who do not learn from \s-1HISTORY\s0 are doomed to repeat it.
.PP
The lesson here is simple: Don't sit next to a Tcl programmer at the
dinner table.
.SH "THANKS"
.IX Header "THANKS"
Thanks to Brent Welch, Damian Conway and Robin Houston.
.SH "AUTHORS"
.IX Header "AUTHORS"
David A Golden <dagolden@cpan.org> (current maintainer)
.PP
Michael G Schwern <schwern@pobox.com> (original author)
.SH "LICENSE"
.IX Header "LICENSE"
Original code Copyright (c) 2001 to 2007 by Michael G Schwern.
Additional code Copyright (c) 2006 to 2008 by David A Golden.
.PP
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
.PP
See http://www.perl.com/perl/misc/Artistic.html
.SH "SEE ALSO"
.IX Header "SEE ALSO"
PadWalker (for the similar idea with lexicals), Hook::LexWrap,
Tcl's \fIuplevel()\fR at http://www.scriptics.com/man/tcl8.4/TclCmd/uplevel.htm