Let's explain what's going on here.

The <=> operator returns -1, 0, or 1 depending on the comparison results. If the terms being compared are equal, zero is returned. Zero also happens to be what Perl thinks of as false. This is important.

The logical short circuit 'or' operator '||' evaluates the left hand side for truth. If the lefthand side evaluates to false, 'or' then looks to the righthand side. This is also important.

Putting it all together... If the lefthand comparison contains unequal terms, the comparison operator returns -1 or 1, both of which are 'true', and the righthand comparison never gets evaluated. If the lefthand comparison contains equal terms, the <=> opearator returns 0 (false), so the || (or) operator then evaluates the expression on the righthand side.

You can chain together multiple expressions this way. The expressions with higher priority should be on the left, and the lower priority should be on the right. The ones further to the right will only be evaluated if the ones further to the left all evaluate to 'equal'.


Dave

In reply to Re^2: Double sort in hash values by davido
in thread Double sort in hash values by rsiedl

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.