Honourable Monks,

I often ponder the performance of the code I am writing, but I do this at a relatively high, algorithmical level. I rarely dig into the intricate world of instructions (be it machine language or Perl bytecode). Recently a question has been forming in my mind: is there a performance hit if you use hash references instead of hashes? Allow me to elaborate. 

%h = qw( ... );
$h = \%h;

# Accessing the hash and the hash reference in a tight loop.
for ( ... ) {
    my $frobnitz = $h{frobnitz};
    my $quark = $h->{quark};
    ...
}

[download]

Is the latter hash access slower than the former, and if so, how much? Does either consume more memory than the other? Should I be aware of other possible overhead? If I have a complex data structure (HoHoHo...), would I be able to squeeze off some performance from using real hashes instead of hash references?

This is not a burning question, because I very rarely write code in Perl where I would need to mind these things. However, I'm curious.

I know I could possibly test this myself with a profiler, but I have yet to read how to use the Perl profiler, or even to figure out which would be a good test scenario.

Thank you for your patience.

--
print "Just Another Perl Adept\n";

In reply to Hash references versus hashes: is there a performance hit? by vrk

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