protocol HasWrappedType { associatedtype WrappedType } extension Optional: HasWrappedType { typealias WrappedType = Wrapped } extension Array where Element: HasWrappedType { func foo() -> Bool { return reduce(true) { $0 && ($1 != nil) } } } let a: [Int?] = [2, 3, 5] print(a.foo()) let b: [Int] = [2, 3, 5] //print(b.foo()) // error: type 'Int' does not conform to protocol 'HasWrappedType'
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