A `SequenceType` Extension for Maybe

[CodaFi]

Recently I recieved this closure reason on a bug report about the false overload of flatMap

This issue behaves as intended based on the following:

Yes, we are aware that this overload of flatMap could be viewed as unconventional. Nevertheless, it is useful and fits the overload set in general, if you view Optional as a sequence of zero or one T. It resembles this overload, where the closure returns an arbitrary sequence:

extension SequenceType {
  public func flatMap<S : SequenceType>(
    transform: (Generator.Element) -> S
  ) -> [S.Generator.Element]
}

The type checker ensures that there is no ambiguity between the two overloads, and we don't see a reason to give one of the overloads a different name (and force users to learn it, and differentiate between the two), since conceptually the operation is the same.

If Swift wishes to regard Optional (rather strangely) as a sequence of 0 or 1 value, I say we let them have their wish and add a SequenceType extension if they won't. As an added bonus, it'll make the SequenceType overloads in Aquifer a bit more general.

[pthariensflame]

:+1: You had the same idea I did after I saw your tweet! :)

[CodaFi]

Fixed by the merge of #246