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Wise monks:

Though I've been using Perl for several years, I've always taken for granted the ease of using hashes in all their incarnations. Now I've returned to school (for a CS degree) and while taking many data structures classes, have been wondering more about what are the internals of Perl's hashes.

I've looked online to find more info on how perl hashing works, and though some articles explain the different hash functions used through different perl versions, it's not clear:

  1. What is the initial size of a hash in memory when created? (e.g. declared "my %hash;", but no data in it yet)
  2. What method is used to "grow" the hash? Doubling & re-hashing? Linear hashing? Something else?

I had written a small Perl script to perform a small task for an algorithms class, and the TA asked me about its true space efficiency versus another method which didn't use hashes, and I realized I couldn't tell him with any confidence how much memory my hash took up.

Any monks familiar with internals that would like to explain it? I suppose I could wade through the source, but... eek! I'm not a C programmer, either. Thanks!

Addendum / Bonus Question: Do Perl hashes differ in implementation versus "associative arrays" that appear in other languages? Do most other languages implement associative arrays internally in hash tables?

In reply to Perl Internals: Hashes by Kozz

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