RCR 344: Implement Hash#hash

Make Hash#hash look at contents just like Array#hash

Array#hash and Hash#hash are inconsistent: Array#hash _does_ look at the contents, while Hash#hash _doesn't_.

For example:

  a = {}
  a[[1,2]] = 10

..now a[[1,2]] gives 10.

  a[{1=>2}] = 11

..now a[{1=>2}] gives nil.

I stumbled upon this while grouping an array of objects based on an aspect (something like Array#sort_by). When I changed the aspect from an Array to an Hash, the grouping stopped working.

Let Hash#hash look at the contents to remove inconsistancy.

This should only effect code which puts hashes in hashes. Currently, there is not much use for that since the keys cannot be retrieved any more except by the initial key, so it should not effect (many) existing programs.

class Hash

    # By default, the hashcode of hash doesn't look at the
    # contents. This makes indexing a hash with a hash impossible.
    def hash
        inject(0) { |h, p| h ^ p[0].hash ^ p[1].hash }
    end
    # When implementing #hash, eql? should be adapted.
    def eql?(other)
        super || other == self
    end

end