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RETURN::MULTILEVEL - reference manual online

Return across multiple call levels.

Chapter
2014-09-07
Return::MultiLevel(3pm)        User Contributed Perl Documentation        Return::MultiLevel(3pm)

NAME Return::MultiLevel - return across multiple call levels
SYNOPSIS use Return::MultiLevel qw(with_return); sub inner { my ($f) = @_; $f->(42); # implicitly return from 'with_return' below print "You don't see this\n"; } sub outer { my ($f) = @_; inner($f); print "You don't see this either\n"; } my $result = with_return { my ($return) = @_; outer($return); die "Not reached"; }; print $result, "\n"; # 42
DESCRIPTION This module provides a way to return immediately from a deeply nested call stack. This is similar to exceptions, but exceptions don't stop automatically at a target frame (and they can be caught by intermediate stack frames using "eval"). In other words, this is more like setjmp(3)/longjmp(3) than "die". Another way to think about it is that the "multi-level return" coderef represents a single-use/upward-only continuation. Functions The following functions are available (and can be imported on demand). with_return BLOCK Executes BLOCK, passing it a code reference (called $return in this description) as a single argument. Returns whatever BLOCK returns. If $return is called, it causes an immediate return from "with_return". Any arguments passed to $return become "with_return"'s return value (if "with_return" is in scalar context, it will return the last argument passed to $return). It is an error to invoke $return after its surrounding BLOCK has finished executing. In particular, it is an error to call $return twice.
DEBUGGING This module uses "unwind" from "Scope::Upper" to do its work. If "Scope::Upper" is not available, it substitutes its own pure Perl implementation. You can force the pure Perl version to be used regardless by setting the environment variable "RETURN_MULTILEVEL_PP" to 1. If you get the error message "Attempt to re-enter dead call frame", that means something has called a $return from outside of its "with_return { ... }" block. You can get a stack trace of where that "with_return" was by setting the environment variable "RETURN_MULTILEVEL_DEBUG" to 1.
BUGS AND LIMITATIONS You can't use this module to return across implicit function calls, such as signal handlers (like $SIG{ALRM}) or destructors ("sub DESTROY { ... }"). These are invoked automatically by perl and not part of the normal call chain.
AUTHOR Lukas Mai, "<l.mai at web.de>" COPYRIGHT & LICENSE Copyright 2013-2014 Lukas Mai. This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License. See http://dev.perl.org/licenses/ for more information.
perl v5.20.1 2014-09-07 Return::MultiLevel(3pm)
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Return::MultiLevel(3pm) referred by
refer to longjmp(3) | setjmp(3)