// *** before: ***
struct PointOld: Hashable {
    let x: Int
    let y: Int

    // the mix was invented by the author, and a weak one turned a Set
    // into a list with linear search
    var hashValue: Int { return x.hashValue ^ y.hashValue }
}

// *** in version 4.2: ***
struct Point: Hashable {
    let x: Int
    let y: Int

    func hash(into hasher: inout Hasher) {
        hasher.combine(x)      // the fields are fed to the standard hasher
        hasher.combine(y)
    }
}

// hashValue is deprecated; the hasher is seeded anew on every run of the
// program, so a hash must not be stored on disk or sent over the network
var hasher = Hasher()
hasher.combine(Point(x: 1, y: 2))
print(hasher.finalize())