Use object_id as hash key can be 20x faster

hash key benchmark

ary= []
30.times do |i|
  ary << {a:1,b:2,c:3,d:4,e:5,f:6,g:7,h:8}
end


Benchmark.bmbm do |x|
  x.report("hash as key") do
    hash = {}
    ary.each do|a| hash[a] = 1 end
    n.times do
      ary.each do|a|
        hash[a]
      end
    end
  end

  x.report("object_id as key") do
    hash = {}
    ary.each do |a| hash[a.object_id] = 1 end
    n.times do
      ary.each do|a|
        hash[a.object_id]
      end
    end
  end
end