coro-modify.swift

struct Stone {
    var x: Int {
        get {
            return 1
        }
        _modify {
            var x: Int = 3
            yield &x
            y = x
        }
    }

    var y: Int = 0
}

func mod(_ x: inout Int) {
    x = 8
}

func main() {
    var a = Stone()
    mod(&a.x)
    print(a.y)
}

main()