hash_methods/key_changing_its_hash.rb

tests/_examples/hash_methods/key_changing_its_hash.rb in the metorex repository.

# A key's own #hash and #eql? may change the hash that is looking it up.
class Key
  attr_reader :name

  def initialize(name, table)
    @name = name
    @table = table
  end

  def hash
    @table[:lookups] = (@table[:lookups] || 0) + 1
    name.hash
  end

  def eql?(other)
    @table[:comparisons] = (@table[:comparisons] || 0) + 1
    other.is_a?(Key) && other.name == name
  end
end

table = {}
first = Key.new("a", table)
table[first] = 1
p(table[Key.new("a", table)])
p(table[Key.new("b", table)])
p(table[:lookups])
p(table.size)

Output:

1
nil
3
3