let arr1 = [1, nil, 3]
print(type(of: arr1))       // Array<Optional<Int>>

struct S {}
let arr2 = [S(), nil]
print(type(of: arr2))       // Array<Optional<S>>

let x1 = true ? 1 : nil
print(type(of: x1))     // Optional<Int>

struct S {}
let x2 = false ? nil : S()
print(type(of: x2))     // Optional<S>

let arr = [(1, "test"), nil, (2, "test")]   // error: type of expression is ambiguous without more context

let c = { $0 * 2 }
let x = true ? c : nil          // error: result values in '? :' expression have mismatching types '(Int) -> Int' and '_'