(Ovid) Re: Orcish Maneuver

[Ovid]

The Orcish Maneuver is a term coined by Joseph Hall in his book "Effective Perl Programming" (co-authored by merlyn). Here's the essence of it:

my @sorted = sort {
    ( $times{$a} ||= -M $a ) <=>
    ( $times{$b} ||= -M $b )
} @old_array;

The "orcish" (a bad attempt at humor: "or cache") maneuver basically caches the results of an expensive lookup using the ||= operator. This operator says, in the above code, that $times{$a} will be evaluated or, if it is false, set it to the value of -M $a. (-M is the file test operator for last modified time). This allows you to cache the results of -M rather than call it every time. This has the same effect as:

for ( @old_array ) {
    $times{ $_ } = -M $_;
}

my @sorted = sort { $times{$a} <=> $times{$b} } @old_array;

Cheers,
Ovid

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