extension Int {
    var isEven: Bool {
        return self % 2 == 0
    }

    var squared: Int {
        return self * self
    }

    func repeated(_ action: () -> Void) {
        for _ in 0..<self {
            action()
        }
    }
}

print(4.isEven)   // true
print(5.squared)  // 25
3.repeated { print("Hi") } // prints Hi three times