ruby_hash_compare_by_identity.rb

irb(main):002> h = {}.compare_by_identity
=> {}
irb(main):003> h['a'] =3
=> 3
irb(main):004> h['a'] =5
=> 5
irb(main):005> h
=> {"a"=>3, "a"=>5}
irb(main):006> h[:a] = 1
=> 1
irb(main):007> h[:a] = 2
=> 2
irb(main):008> h
=> {"a"=>3, "a"=>5, :a=>2}
irb(main):009> h["a"]
=> nil
irb(main):011> x = h.first[0]
=> "a"
irb(main):012> h[x]
=> 3
irb(main):014* h.each do |k,v|
irb(main):015*   puts "#{k} - #{h[k]}"
irb(main):016> end
a - 3
a - 5
a - 2
=> {"a"=>3, "a"=>5, :a=>2}