Re: "next" in Parallel::ForkManager, and subroutines

You use next to jump out of a sub. That's fine. It's supported.

Minimal example:

use 5.010;
use strict;

sub my_sub { next };

for (1..5)
{
    say "Hello";
    my_sub();
    say "World";
}
[download]

This says "Hello" five times, but does not say "World" because the sub my_sub calls next.

While it's supported by Perl, it's also considered a slightly odd thing to do - and quite non-obvious (the sub my_sub could be defined hundreds of lines away from the loop which uses it, or even in another file), so Perl warns you about it, just in case you're doing it accidentally. If you run my example with warnings switched on, you'll get five warnings about exiting the sub using next, but these are just warnings, not errors. The script prints out a warning, but keeps on running.

If you're doing it deliberately, and don't want to be warned about it then:

no warnings qw[exiting];
[download]

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

Comment on Re: "next" in Parallel::ForkManager, and subroutines Select or Download Code

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Re^2: "next" in Parallel::ForkManager, and subroutines by thargas (Deacon) on Apr 04, 2012 at 18:56 UTC
Hmm. The docs for `next` include: `"next" cannot be used to exit a block which returns a value such as "eval {}", "sub {}" or "do {}", and should not be used to exit a grep() or map() operation.` [download] Doesn't sound supported to me.	[reply] [d/l] [select]
Re^3: "next" in Parallel::ForkManager, and subroutines by tobyink (Canon) on Apr 23, 2012 at 10:07 UTC
I think this is referring to the fact that you can't use `next` to "just" jump out of a `sub` (or `do` or `eval`) - it needs to jump out of another block (which does not return a value) at a higher level. Compare this: `sub foo () { next } foo` [download] with this: `sub foo () { next } foo for 1` [download] The first dies with Can't "next" outside a loop block; the second runs successfully, but will warn when warnings are enabled. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]