From: "Shot (Piotr Szotkowski)" <shot@...>
Date: 2007-01-30T07:38:20+09:00
Subject: Sane #hash implementation?

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I have a Set subclass, Block. I need two blocks to be considered the
same by Set iff they have the same elements. From what I gathered, Set
treats two objects as equal when they are eql? and have the same hash.

Implementing Block#eql? seems to be trivial, as Set#=3D=3D is there to help:

class Block < Set
  def eql? other
    self =3D=3D other
  end
end

I=E2=80=99m stuck when it comes to Block#hash, though; I need these to be t=
rue:
Block.new.hash =3D=3D Block.new.hash
Block.new([1,2]).hash =3D=3D Block.new([1,2]).hash

What=E2=80=99s the proper way to go at it? Adding the elements=E2=80=99 has=
hes together
is obviously wrong, as four different elements might produce the same
sum when paired; also, the docs say, =E2=80=98any hash value that exceeds t=
he
capacity of a Fixnum will be truncated before being used,=E2=80=99 so hash =
can=E2=80=99t
exceed the (word - 1 bit) size.

-- Shot
--=20
Hell hath no fury like a bureaucrat scorned.   -- Milton Friedman

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