Beefy Boxes and Bandwidth Generously Provided by pair Networks
laziness, impatience, and hubris

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

It's someone being less clever than they think they are. They think that:

  • $cache being assigned undef is an expensive operation, so by using "if undef", which is always false, we'll save on the actual assignment, and since perl already guarantees an uninitialised variable to be undef, it'll still be undef. This is supposedly more readable since you can still see $cache is set to undef. I would disagree - the "if undef" part is just plain confusing and should be removed. Whether you want to leave the assignment, "= undef", or not, is a matter of personal taste. In cases like this, I probably would leave it in, again, to make it explicit, but others like to play golf a bit more than I do, and would tell you to remove it, too - doesn't really matter.
  • The original author also thought that this would have $cache be static or something, and so we'd generate the cache only once, no matter how many times it's called. They're definitely wrong here, too. A couple of options - move the "my $cache" line to outside the sub, or do that and also put braces around the whole thing. As an example of the latter:
    { my $cache = undef; sub IsMatrix { shift if UNIVERSAL::isa($_[0], __PACKAGE__); my ($child, $parent) = @_; unless ($cache) { my %cache; @cache{@matrices} = (1) x scalar(@matrices); $cache = \%cache; } + return $cache->{"${child}_$parent"}; } }
    The outter braces are the optional part. With them, $cache is only visible inside IsMatrix, without them, the variable is visible to the entire file. With the braces is closer to the original author's intent, but I'm not sure the original author's intent is really that important given these mistakes ;-)
Hope that helps.

In reply to Re: my $cache = undef if undef; by Tanktalus
in thread my $cache = undef if undef; by szabgab

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!
  • 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, 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, 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.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others browsing the Monastery: (10)
    As of 2015-10-13 13:53 GMT
    Find Nodes?
      Voting Booth?

      Does Humor Belong in Programming?

      Results (307 votes), past polls