swift-evolutionの"[swift-evolution] [Pitch] Revamp Optional and Throws" スレッドでのJohn McCallのコメント。コアチーム（の中でもエラーハンドリング分野で一番影響力がありそうなJohn）の考えが知れておもしろい。
We've definitely considered including a Result type, but our sense was that in an ideal world almost no code would be using it. It's hard to imagine an ordinary API that ought to be returning a Result rather than throwing, and once you've defined that away, the major remaining use case is just to shift computation around, like with a completion handler. That explicit computation-shifting pattern is something we're hoping to largely define away with something like C#'s async/await, which would leave Result as mostly just an implementation detail of such APIs. We didn't want to spend a great deal of time designing a type that would end up being so marginal, especially if the changing role would lead us into different directions on the design itself. We also didn't want to design a type that would become an obstacle to potential future language changes like, say, typed throws. The downside, of course, is that as long as we lack that async/await design, computation-shifting isn't real great.