Should the following two lines of code do the same thing? 

$hash{$_} ||= 1 + keys %hash for @list;
$hash{$_} = $hash{$_} || 1 + keys %hash for @list;

[download]

IMO the second one should be well defined. tye and diotalevi think that both are undefined, I could be conviced about the first, but I need more convincing on the second.

This came up because I was being cheeky in Re^3: Perl one-liner to remove duplicate entries from PATH and wound up scratching my head. 

use Data::Dump::Streamer;
my (%hash,%mash);
@list=('A'..'C');
$hash{$_} ||= 1 + keys %hash for @list;
$mash{$_} = $mash{$_} || 1 + keys %mash for @list;
Dump(\%hash,\%mash)->Names('*hash','*mash')->Out();
__END__
%hash = (
          A => 2,
          B => 3,
          C => 4
        );
%mash = (
          A => 1,
          B => 2,
          C => 3
        );

[download]
---
$world=~s/war/peace/g

In reply to Are "$hash{$_} ||= 1 + keys %hash" and variants well defined or not? by demerphq

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.