การเปลี่ยนแปลงค่าและการกำหนด self ใหม่

struct Point {
    var x = 0
    var y = 0
    mutating func reset() {
        self = Point(x: 0, y: 0)
    }
}
var p = Point(x: 3, y: 4)
p.reset()
print(p.x, p.y)

struct Vector {
    var dx: Int
    var dy: Int
    mutating func negate() {
        self = Vector(dx: -dx, dy: -dy)
    }
}
var v = Vector(dx: 2, dy: -3)
v.negate()
print(v.dx, v.dy)

enum State {
    case idle, running, done
    mutating func advance() {
        switch self {
        case .idle: self = .running
        case .running: self = .done
        case .done: self = .done
        }
    }
}
var s = State.idle
s.advance()
s.advance()
print(s)

struct Point {
    var x = 0
    var y = 0
    mutating func setBoth(_ n: Int) {
        self = Point(x: n, y: n)
    }
}
var p = Point()
p.setBoth(7)
print(p.x, p.y)

struct Counter {
    var value: Int
    mutating func doubled() {
        self = Counter(value: value * 2)
    }
}
var c = Counter(value: 5)
c.doubled()
print(c.value)

struct Temperature {
    var celsius: Double
    mutating func toRounded() {
        self = Temperature(celsius: celsius.rounded())
    }
}
var t = Temperature(celsius: 21.7)
t.toRounded()
print(t.celsius)

struct Flag {
    var on = false
    mutating func turnOn() {
        self = Flag(on: true)
    }
}
var f = Flag()
f.turnOn()
print(f.on)

struct Score {
    var points: Int
    mutating func clamp() {
        if points > 100 {
            self = Score(points: 100)
        }
    }
}
var s = Score(points: 150)
s.clamp()
print(s.points)

enum Switch {
    case off, on
    mutating func flip() {
        self = (self == .off) ? .on : .off
    }
}
var sw = Switch.off
sw.flip()
print(sw)

struct Box { var n: Int; mutating func zero() { self = Box(n: 0) } }
var a = Box(n: 5)
var b = a
a.zero()
print(a.n, b.n)

struct Pair {
    var a: Int
    var b: Int
    mutating func swapValues() {
        self = Pair(a: b, b: a)
    }
}
var p = Pair(a: 1, b: 2)
p.swapValues()
print(p.a, p.b)

enum T { case a, b; mutating func go() { self = .b } }
var t = T.a
t.go()
print(t)