I tried to avoid renaming: https://github.com/apple/swift/pull/7823/ but then https://github.com/apple/swift/pull/9390.

一回警告出るようなパッチ当てたけど外したとのこと。

[stdlib] Adding a deprecated version of flatMap to warn misuses. by moiseev · Pull Request #7823 · apple/swift

Due to implicit promotion to optional it is possible to call flatMap with a closure, that does not return an optional. This way the code works, but is unnecessary inefficient. Such uses of flatMap ...

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1:56 AM

これはflatMap(E->T)をオーバーロードしてdeprecatedつけてるね。かしこそう。