koher

extension Optional { @_specialize(exported: true, where 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:2:6: error: too few type parameters are specified in '_specialize' attribute (got 1, but expected 2) @_specialize(exported: true, where S == [Int]) ^ /usercode/main.swift:2:6: error: Missing constraint for 'Wrapped' in '_specialize' attribute @_specialize(exported: true, where S == [Int]) ^