Re: Hash tables, are they really what we see?

[dsheroh]

But let`s assume we have a hash with, for example over 1 000 000 entries as a word count and we then search for a word that just does not appear there? How in blazes Perl will know that there is not that word from a million of words!? I just picture a barrel filled with red and blue balls over a million and you have to tell that you are 100% there is no other colors by just looking at that barrel.

Your barrel is the wrong image for visualizing a hash. The magic of hashes is that you don't do hash searches, you do hash lookups. When you ask for $hash{foo}, Perl doesn't have to examine every key in %hash to see whether foo is among them, instead, it calculates "If a key foo exists, then it will be in this location.", then looks only in that location.

For a better real-world image, think of a hotel with mailboxes on the wall behind the front desk. When you want to see whether you have any mail, you don't tell the clerk your name and then wait for them to check every piece of mail to see who it's addressed to. Instead you say "I'm in room 234" and the clerk looks only at the box numbered 234. If there's anything in that box, you have mail; if there isn't, you don't. (In this example, you stating your room number is analogous to the hashing function used by Perl to map hash keys to "buckets" in the hash.)