class Hash

def deep_dup

dup[:a][:c] #=> "c"
hash[:a][:c] #=> nil

dup[:a][:c] = 'c'
dup = hash.deep_dup
hash = { a: { b: 'b' } }

Returns a deep copy of hash. 
def deep_dup
  each_with_object(dup) do |(key, value), hash|
    hash[key.deep_dup] = value.deep_dup
  end
end