gistfile1.txt

struct Value {
    var property: Int = 0

    mutating func change() {
        property++
    }

    func changed() -> Value {
        var copy = self
        copy.property++
        return copy
    }
}

var a = Value()
a.property // 0
a.change()
a.property // 1
a = a.changed()
a.property // 2