Sub::Uplevel(3pm)

1Sub::Uplevel(3)       User Contributed Perl Documentation      Sub::Uplevel(3)
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NAME

6       Sub::Uplevel - apparently run a function in a higher stack frame
7

SYNOPSIS

9         use Sub::Uplevel;
10
11         sub foo {
12             print join " - ", caller;
13         }
14
15         sub bar {
16             uplevel 1, \&foo;
17         }
18
19         #line 11
20         bar();    # main - foo.plx - 11
21

DESCRIPTION

23       Like Tcl's uplevel() function, but not quite so dangerous.  The idea is
24       just to fool caller().  All the really naughty bits of Tcl's uplevel()
25       are avoided.
26
27       THIS IS NOT THE SORT OF THING YOU WANT TO DO EVERYDAY
28
29       uplevel
30             uplevel $num_frames, \&func, @args;
31
32           Makes the given function think it's being executed $num_frames
33           higher than the current stack level.  So when they use
34           caller($frames) it will actually give caller($frames + $num_frames)
35           for them.
36
37           "uplevel(1, \&some_func, @_)" is effectively "goto &some_func" but
38           you don't immediately exit the current subroutine.  So while you
39           can't do this:
40
41               sub wrapper {
42                   print "Before\n";
43                   goto &some_func;
44                   print "After\n";
45               }
46
47           you can do this:
48
49               sub wrapper {
50                   print "Before\n";
51                   my @out = uplevel 1, &some_func;
52                   print "After\n";
53                   return @out;
54               }
55
56           "uplevel" will issue a warning if $num_frames is more than the
57           current call stack depth.
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EXAMPLE

60       The main reason I wrote this module is so I could write wrappers around
61       functions and they wouldn't be aware they've been wrapped.
62
63           use Sub::Uplevel;
64
65           my $original_foo = \&foo;
66
67           *foo = sub {
68               my @output = uplevel 1, $original_foo;
69               print "foo() returned:  @output";
70               return @output;
71           };
72
73       If this code frightens you you should not use this module.
74

BUGS and CAVEATS

76       Well, the bad news is uplevel() is about 5 times slower than a normal
77       function call.  XS implementation anyone?  It also slows down every
78       invocation of caller(), regardless of whether uplevel() is in effect.
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80       Sub::Uplevel overrides CORE::GLOBAL::caller temporarily for the scope
81       of each uplevel call.  It does its best to work with any previously
82       existing CORE::GLOBAL::caller (both when Sub::Uplevel is first loaded
83       and within each uplevel call) such as from Contextual::Return or
84       Hook::LexWrap.
85
86       However, if you are routinely using multiple modules that override
87       CORE::GLOBAL::caller, you are probably asking for trouble.
88
89       You should load Sub::Uplevel as early as possible within your program.
90       As with all CORE::GLOBAL overloading, the overload will not affect
91       modules that have already been compiled prior to the overload.  One
92       module that often is unavoidably loaded prior to Sub::Uplevel is
93       Exporter.  To forceably recompile Exporter (and Exporter::Heavy) after
94       loading Sub::Uplevel, use it with the ":aggressive" tag:
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96           use Sub::Uplevel qw/:aggressive/;
97
98       The private function "Sub::Uplevel::_force_reload()" may be passed a
99       list of additional modules to reload if ":aggressive" is not aggressive
100       enough.  Reloading modules may break things, so only use this as a last
101       resort.
102
103       As of version 0.20, Sub::Uplevel requires Perl 5.6 or greater.
104

HISTORY

106       Those who do not learn from HISTORY are doomed to repeat it.
107
108       The lesson here is simple:  Don't sit next to a Tcl programmer at the
109       dinner table.
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THANKS

112       Thanks to Brent Welch, Damian Conway and Robin Houston.
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AUTHORS

115       David A Golden <dagolden@cpan.org> (current maintainer)
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117       Michael G Schwern <schwern@pobox.com> (original author)
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LICENSE

120       Original code Copyright (c) 2001 to 2007 by Michael G Schwern.
121       Additional code Copyright (c) 2006 to 2008 by David A Golden.
122
123       This program is free software; you can redistribute it and/or modify it
124       under the same terms as Perl itself.
125
126       See http://www.perl.com/perl/misc/Artistic.html
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