if ($_ eq 'A' || $_ eq 'B' || $_ eq 'C') { }

[download]
is the same as 
if ({A =>1, B =>1, C =>1}->{$_}) { }

[download]
is the same as 
if (/^(A|B|C)$/) { }

[download]
 if (/^(A|B|C)\z/) { } or even better, if (/^(?:A|B|C)\z/) { } is the same as 
my $chr = $_;
grep { $chr eq $_ } qw( a b c );

[download]

Benchmarking, it seems the anonymous hash method is slightly faster than ||, but slower than /^()$/, which is also more terse and probably uses less memory. Regex wins again!

Editor's note: $ should be \z in regex as pointed out by ysth and ikegami. Also see ikegami's response for regex improvement and benchmark contestment.

Edit: Added diotalevi's grep suggestion for extra TMTOWTDI fun.

In reply to Collapsing repetitive equality tests: || vs {} vs // (an observation) by blogical

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.