なるほど

infix operator => public func =><T, U>(lhs: T, rhs: (T) throws -> U) rethrows -> U { return try rhs(lhs) } extension Sequence { func reduce<A>(into initial: A, _ combine: (inout A, Iterator.Element) -> ()) -> A { var result = initial for element in self { combine(&result, element) } return result } } let strings = ["a:2", "b:3", "c:5"] let dictionary = strings.reduce(into: [:]) { (r: inout [Int: String], e) in e.components(separatedBy: ":") => { r[$0[0]] = Int($0[1])! } }

error: cannot subscript a value of incorrect or ambiguous type e.components(separatedBy: ":") => { r[$0[0]] = Int($0[1])! } ^~

型推測しきれないぽい。 (edited)