enum E { case A(Int, String) case B(String, Float) } func foo(e: E) { switch e { case .A(_, let str): // something. fallthrough case .B(let str, _): print(str) } }

これが通るようになるらしいです。 https://github.com/apple/swift/pull/14041/files#diff-3f455e97fae02f7b158f90077919c17fR140

[Sema/SILGen] Support for fallthrough into cases with pattern variables. by gregomni · Pull Request #14041 · apple/swift

This is the simplest / most-restrictive version of this feature. The previous case that we're falling from must have a superset of the bindings of the case we're falling into and all the to-case bi...