assert_valid_keys slow?

I don't know if this is helpful or not, but I figured I would share it.

I am writing a library that uses ActiveSupport. I have been using the Hash.assert_valid_keys method in various parts throughout the library. What was really surprising was when I started profiling the library to try and increase performance. The Hash.assert_valid_keys method was my biggest bottle neck.

A test that once took 19.2 seconds is now taking 12.6 seconds once I stopped using Hash.assert_valid_keys. The culprit is Array.flatten. I rewrote the method and got a 35% performance increase.

def fast_assert_valid_keys(valid_keys)
  unknown_keys = keys - valid_keys
  raise(ArgumentError, "Unknown key(s): #{unknown_keys.join(", ")}") unless unknown_keys.empty?
end

I know this changes how the method is used and what kind of arguments it takes, but I thought a 35% increase was significant enough to report.

I don't mean to nitpick either.

Thanks!