Strategy.swift

class Sequence {
    private var numbers: [Int]
    
    init(_ numbers: Int...) {
        self.numbers = numbers
    }
    
    func addNumber(value: Int) {
        self.numbers.append(value)
    }
    
    func compute() -> Int {
        return numbers.reduce(0, combine: { $0 + $1})
    }
}

let sequece = Sequence(1, 2, 3, 4, 5)
sequece.addNumber(10)
sequece.addNumber(20)

let sum = sequece.compute()
print("Sum: \(sum)")