1> extension Array where Element == Optional<Any> { 2. func foo() -> Bool { 3. return reduce(true) { 4. $0 && ($1 != nil) 5. } 6. } 7. } 8> let a: [Int?] = [2, 3, 5] 9. print(a.foo()) error: repl.swift:9:7: error: '[Int?]' is not convertible to 'Array<Optional<Any>>' print(a.foo()) ^