hurricup has asked for the wisdom of the Perl Monks concerning the following question:

Perldoc says pretty same for them, like

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.

I read cannot as doesn't work. But. In some modules, like Par::Dist I can see code like:

File::Find::find( sub {
        next unless $File::Find::name;
        (-r && !-d) and push ( @files, substr($File::Find::name, 5) );
    } , 'blib' );

[download]

What is it? Outdated documentation? Do I get cannot wrong way? Some tricky next, like sub?

Also, TIL, missing in docs, that last/next/redo may be used in statement modifiers, like say $_ and last for 1,2,3

I'm working on new code inspection, so question is not rythorical.

Replies are listed 'Best First'.
Re: last/next/redo usages
by haukex (Archbishop) on Mar 20, 2018 at 20:36 UTC

    Good question where it's documented, but yes, it is possible, although it warns:

    use warnings;
use strict;
use diagnostics;

sub foo { last if /e/; next if /c/; redo if s/b/B/ }

my @x = qw/a b c d e f/;
for (@x) {
    foo;
    print "$_\n";
}

__END__
a
Exiting subroutine via redo at test.pl line 6 (#1)
    (W exiting) You are exiting a subroutine by unconventional means, 
+such
    as a goto, or a loop control statement.
    
B
Exiting subroutine via next at test.pl line 6 (#1)
d
Exiting subroutine via last at test.pl line 6 (#1)

    [download]

    Update: See also e.g. Exiting subroutine via next

[reply]
[d/l]

      Here is related bug and devs discussion.

[reply]
Re: last/next/redo usages
by LanX (Saint) on Mar 20, 2018 at 23:32 UTC
    I seem to remember that last/next/redo are implemented as edge cases of goto LABEL.

    Provided the target label is set it's possible to goto out of a sub into a scope in the dynamic caller chain. (One use case is to short circuit leaving a recursion, without needing to step thru hundreds of returns*)

    So this behavior doesn't surprise me. (Though I would have expected to see a label)

    My bet is the documentation is wrong or badly worded or at least outdated.

    Cheers Rolf
    (addicted to the Perl Programming Language and ☆☆☆☆ :)
    Wikisyntax for the Monastery

    update

    *) demo 

    use strict;
use warnings;
use 5.12.0;


sub count_down {
   my ($a)=@_;
   say --$a;
   goto EXIT unless $a;
   count_down($a)
}


count_down(10);

say "never reached";

EXIT:
say "byebye";

    [download]

    9
8
7
6
5
4
3
2
1
0
byebye

    [download]
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Re: last/next/redo usages
by stevieb (Canon) on Mar 22, 2018 at 01:17 UTC

    I suspect, after realizing the author of the post, that this is research for either the IntelliJ Perl plugin, or the associated IDE debug CPAN integration.

    Kudos hurricup, you've done a spectacular job, and I must admit, that you've allowed me to streamline my C, C++, C#, Python and Perl programming tremendously by authoring your software.

    Please keep up keeping up on such wonderful work.

    (I normally don't praise anyone so loudly, but definitely ++).

    Thankfully you've come to the best of places to get feedback on such research.

    -stevieb

[reply]

      Yes, it is for new inspection in the plugin and thank you, glad that plugin helps!

[reply]

        Any one of my CPAN distributions I've added or edited within the last two-or-so years have been worked on wholly or at least partially using your plugin, and I've even gone as far as to have acquired a JetBrains Open Source license for their entire software suite thanks to the integration of Perl with their tools. (I just recently (February) received my second consecutive one-year-term OS license from them).

        The Open Source license is technically assigned to my berrybrew work, but if it weren't for your dedication to the IntelliJ platform, even though I use PyCharm professional for $work, I wouldn't even have learned about their Open Source dedication.

        Thanks again hurricup.

[reply]
[d/l]
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