resettable.swift

protocol Resettable {
    mutating func reset()
    init()
}

extension Resettable {
    mutating func reset() {
        self = Self() // Assigning to 'self'.
    }
}

class Foo : Resettable {
    var value: Int
    required init() {
        value = 0
    }
}

var ref1 = Foo()
let ref2 = ref1
assert(ObjectIdentifier(ref1) == ObjectIdentifier(ref2))

ref1.value = 42
assert(ObjectIdentifier(ref1) == ObjectIdentifier(ref2))

ref1.reset()
assert(ObjectIdentifier(ref1) != ObjectIdentifier(ref2))
assert(ref1.value == 0)
assert(ref2.value == 42)