$ xcrun --toolchain org.swift.4020170523a swift Welcome to Apple Swift version 4.0-dev (LLVM 351dc0fd49, Clang 9cf11ef2d0, Swift 3ea9a3bac7). Type :help for assistance. 1> struct S {} 2. let mapped = zip([S()], [""]).map { 3. ((s, string)) -> S in s 4. } error: repl.swift:3:6: error: closure tuple parameter does not support destructuring ((s, string)) -> S in s ^~~~~~~~~~~ arg0 let (s, string) = arg0;

Swift 4のタプル周りの変更、なかなか面倒だ。 (edited)