I don’t want constants. I want immutability. The problem isn’t someone reassigning FOO. It’s them changing the data that FOO represents. So I’d love to just use

I don’t want constants. I want immutability. The problem isn’t someone reassigning FOO. It’s them changing the data that FOO represents. So I’d love to just use Python and pass around tuples, strings, frozensets and a homemade frozendict, but the performance is terrible. Any change means a full copy of the whole data structure.