MyFunctionalMethod.swift

extension Int {
    func doMath(_ transform: ((Int) -> (Int)) ) -> (Int) {
        return transform(self)
    }
}

let doubled = 5.doMath { (number) -> (Int) in
    return number * 2
}
print(doubled) // 10

let minusOne = 8.doMath { $0 - 1 }
print(minusOne) // 7