koher

extension Optional { @_specialize(exported: true, where Wrapped == Int, S == [Int]) func foo<S : Sequence>(_ sequence: S) -> [Wrapped] where S.Element == Wrapped { return Array(sequence) + (self.map { [$0] } ?? []) } }

Version:

swift-4.1.1-RELEASE

Output:

Error:

/usercode/main.swift:2:48: warning: redundant same-type constraint 'Wrapped' == 'Int' @_specialize(exported: true, where Wrapped == Int, S == [Int]) ^ /usercode/main.swift:2:58: note: same-type constraint 'S.Element' == 'Int' implied here @_specialize(exported: true, where Wrapped == Int, S == [Int]) ^