--- /dev/null
+# Generated by Pod::WikiDoc version 0.18
+
+=pod
+
+=head1 NAME
+
+Sub::Uplevel - apparently run a function in a higher stack frame
+
+=head1 VERSION
+
+This documentation describes version 0.1901
+
+
+=head1 SYNOPSIS
+
+ use Sub::Uplevel;
+
+ sub foo {
+ print join " - ", caller;
+ }
+
+ sub bar {
+ uplevel 1, \&foo;
+ }
+
+ #line 11
+ bar(); # main - foo.plx - 11
+
+=head1 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.
+
+B<THIS IS NOT THE SORT OF THING YOU WANT TO DO EVERYDAY>
+
+=over 4
+
+=item B<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.
+
+C<uplevel(1, \&some_func, @_)> is effectively C<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;
+ }
+
+
+=begin _private
+
+So it has to work like this:
+
+ Call stack Actual uplevel 1
+CORE::GLOBAL::caller
+Carp::short_error_loc 0
+Carp::shortmess_heavy 1 0
+Carp::croak 2 1
+try_croak 3 2
+uplevel 4
+function_that_called_uplevel 5
+caller_we_want_to_see 6 3
+its_caller 7 4
+
+So when caller(X) winds up below uplevel(), it only has to use
+CORE::caller(X+1) (to skip CORE::GLOBAL::caller). But when caller(X)
+winds up no or above uplevel(), it's CORE::caller(X+1+uplevel+1).
+
+Which means I'm probably going to have to do something nasty like walk
+up the call stack on each caller() to see if I'm going to wind up
+before or after Sub::Uplevel::uplevel().
+
+=end _private
+
+=begin _dagolden
+
+I found the description above a bit confusing. Instead, this is the logic
+that I found clearer when CORE::GLOBAL::caller is invoked and we have to
+walk up the call stack:
+
+* if searching up to the requested height in the real call stack doesn't find
+a call to uplevel, then we can return the result at that height in the
+call stack
+
+* if we find a call to uplevel, we need to keep searching upwards beyond the
+requested height at least by the amount of upleveling requested for that
+call to uplevel (from the Up_Frames stack set during the uplevel call)
+
+* additionally, we need to hide the uplevel subroutine call, too, so we search
+upwards one more level for each call to uplevel
+
+* when we've reached the top of the search, we want to return that frame
+in the call stack, i.e. the requested height plus any uplevel adjustments
+found during the search
+
+=end _dagolden
+
+=back
+
+=head1 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 B<you should not use this module.>
+
+
+=head1 BUGS and CAVEATS
+
+Well, the bad news is uplevel() is about 5 times slower than a normal
+function call. XS implementation anyone?
+
+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.
+
+=head1 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.
+
+=head1 THANKS
+
+Thanks to Brent Welch, Damian Conway and Robin Houston.
+
+=head1 AUTHORS
+
+David A Golden E<lt>dagolden@cpan.orgE<gt> (current maintainer)
+
+Michael G Schwern E<lt>schwern@pobox.comE<gt> (original author)
+
+=head1 LICENSE
+
+Original code Copyright (c) 2001 to 2007 by Michael G Schwern.
+Additional code Copyright (c) 2006 to 2008 by David A Golden.
+
+This program is free software; you can redistribute it and/or modify it
+under the same terms as Perl itself.
+
+See http://www.perl.com/perl/misc/Artistic.html
+
+=head1 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
+
projects / dh-make-perl / blobdiff