hash_nested_merge.rb

class Hash
  def nested_merge(other)
    result = self
    other.each do |key, value|
      if Hash === self[key] && Hash === other[key]
        result[key] = self[key].nested_merge(other[key])
      else
        result[key] = other[key]
      end
    end
    result
  end
end

describe Hash, :nested_merge do
  it "should return a merged hash" do
    a = {:a => 1, :b => {:c => 1, :d => {:foo => 'bar'}, :abc => 'boo'}}
    b = {:a => 2, :b => {:c => 'x', :d => {:foo => 'xx'}}, :y => 'y'}
    a.nested_merge(b).should ==
        {
          :a => 2,
          :b => {
            :c => 'x',
            :d => {:foo => 'xx'},
            :abc => 'boo'
          },
          :y => 'y'
        }
  end
end