I have tried to boil this issue down to its simplest form with the following.
Xcode Version 6.1.1 (6A2008a)
An enum defined in MyEnum.swift
MyEnum.swift
Add this to your code:
extension MyEnum { init?(rawValue: Int) { switch rawValue { case 0: self = .Zero case 1: self = .One case 2: self = .Two default: return nil } } }