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Re: elsif chain vs. dispatch

by almut (Canon)
on Apr 26, 2009 at 22:23 UTC ( #760206=note: print w/ replies, xml ) Need Help??

in reply to elsif chain vs. dispatch

If you don't recreate the dispatch table upon every invocation of dispatch() by placing it outside of the routine, the difference already is much smaller:

Rate dispatch elsif dispatch 9363/s -- -12% elsif 10627/s 13% --

even though in that case, there's still a disadvantage on the side of the dispatch table, because the $y needs to be passed to the anonymous sub...

my %dispatch=( A=>sub { split(/!/,$_[0]); }, ... ); sub dispatch { my $x=$letters[random($nLetters)]; my $y='xyzzy!' x random(1000); if (exists $dispatch{$x}) { $dispatch{$x}->($y); } else { warn "Huh?"; } }

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Re^2: elsif chain vs. dispatch
by ruzam (Curate) on Apr 27, 2009 at 02:40 UTC

    $y could be passed as a reference to avoid the string copy further reduce the disadvantage, particularly for large strings.

    my %dispatch=( A=>sub { split(/!/,$$_[0]); }, ... ); sub dispatch { my $x=$letters[random($nLetters)]; my $y='xyzzy!' x random(1000); if (exists $dispatch{$x}) { $dispatch{$x}->(\$y); } else { warn "Huh?"; } }

    On the other hand, maybe the parameter string isn't copied when the function references $_[0] directly?

      I had tried that.  And had first made the same mistake (and thus got a speed boost of around 800% :) —> the $$_[0] would need to be ${$_[0]}. With that fixed, there's virtually no difference...   In other words, the string isn't copied, even without using references ($_[0] is an alias).

        Interesting. Now I've got some code to review that may stand for another tweak or two :)

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