Hi guys,

I just noticed that the given/when construct's way of introducing a lexical $_ plays badly with functions that take BLOCKs such as List::MoreUtils::any. The following does not print anything:

use 5.010;
use strict;
use warnings;
use List::MoreUtils qw/ any /;

my $s = "foo";
my @list = ( 1, undef, 2 );
given($s) {
    when('foo') {
        say "found undef" if any { ! defined($_) } @list;
    }
}

[download]

Within the block, $_ is always 'foo' as it was bound during the block's definition.

Now this must be a known problem, right? For my inner peace, could someone explain me the rationale for making "given" so subtly different from say "for"? And for my productivity, is there a way around it short of "don't use 'given'"?

Thanks very much!

In reply to Lexical $_ in given/when vs. BLOCK arguments by mbethke

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.