// *** before: ***
func doubledOld(_ value: Int) -> Int {
    return value * 2
}

struct RectangleOld {
    var width = 2.0
    var height = 3.0
    var area: Double { return width * height }
}

// *** in version 5.1: ***
func doubled(_ value: Int) -> Int { value * 2 }

struct Rectangle {
    var width = 2.0
    var height = 3.0
    var area: Double { width * height }
}

extension Array {
    var second: Element? { count > 1 ? self[1] : nil }
}

// a closure has behaved this way since the very first Swift; now a function,
// a property and a subscript follow the same rule