もうSwift 4.0.1へ入れてもらえないと諦めていた修正が入りそうで嬉しい。 https://github.com/apple/swift/pull/12369

[4.0] Remove previous hack for SR-5206 by itaiferber · Pull Request #12369 · apple/swift

What's in this pull request? Cherry-picks #11315 to swift-4.0-branch. Explanation: Better resolves SR-5206 until the introduction of conditional conformance. As a temporary workaround for SR-5206, ...