Learn from flutter hashValues – no recursion, more better

[kevmoo]

See https://github.com/flutter/engine/blob/52bbe398a5f1d77651e3f017fd5be6cf26afd705/lib/ui/hash_codes.dart

[kevmoo]

CC @davidmorgan

[davidmorgan]

Fun. I guess what built_value generates now, e.g.

https://github.com/google/built_value.dart/blob/master/example/lib/collections.g.dart#L63

is a tiny bit faster, no optional parameters or if statements -- but costs a little code size.

[kevmoo]

@davidmorgan When you know statically what the number of args is, sure.

[davidmorgan]

Yes. Just making the point that generation is always going to be better :) ... source_gen FTW.

Still makes sense for quiver, though.