| Return::MultiLevel(3pm) | User Contributed Perl Documentation | Return::MultiLevel(3pm) |
Return::MultiLevel - Return across multiple call levels
version 0.08
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
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.
The following functions are available (and can be imported on demand).
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.
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.
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.
This software is copyright (c) 2013,2014,2021 by Lukas Mai.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
| 2021-12-25 | perl v5.32.1 |