CODESAMPLE

Strategy - Swift

Strategy Swift

The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It allows an algorithm to vary independently from the clients that use it. In this Swift implementation, we define a protocol SortingStrategy with a single method sort. Different concrete strategies like BubbleSortStrategy and QuickSortStrategy conform to this protocol, each implementing a distinct sorting algorithm. A Sorter class uses a SortingStrategy instance to perform the sorting, delegating the actual sorting logic. This is idiomatic Swift due to its strong use of protocols for defining behavior and dependency injection for achieving flexibility.

// Define the Strategy interface (Protocol)
protocol SortingStrategy {
    func sort(list: [Int]) -> [Int]
}

// Concrete Strategies
struct BubbleSortStrategy: SortingStrategy {
    func sort(list: [Int]) -> [Int] {
        var sortedList = list
        let n = sortedList.count
        for i in 0..<n {
            for j in 0..<n-i-1 {
                if sortedList[j] > sortedList[j+1] {
                    sortedList.swapAt(j, j+1)
                }
            }
        }
        return sortedList
    }
}

struct QuickSortStrategy: SortingStrategy {
    func sort(list: [Int]) -> [Int] {
        guard list.count > 1 else { return list }
        let pivot = list[0]
        let less = list.filter { $0 < pivot }
        let equal = list.filter { $0 == pivot }
        let greater = list.filter { $0 > pivot }
        return QuickSortStrategy().sort(list: less) + equal + QuickSortStrategy().sort(list: greater)
    }
}

// Context
class Sorter {
    private var strategy: SortingStrategy

    init(strategy: SortingStrategy) {
        self.strategy = strategy
    }

    func setStrategy(strategy: SortingStrategy) {
        self.strategy = strategy
    }

    func sortList(list: [Int]) -> [Int] {
        return strategy.sort(list: list)
    }
}

// Usage
let myList = [5, 1, 4, 2, 8]

// Use Bubble Sort
var bubbleSorter = Sorter(strategy: BubbleSortStrategy())
let sortedBubble = bubbleSorter.sortList(list: myList)
print("Bubble Sort: \(sortedBubble)")

// Switch to Quick Sort
bubbleSorter.setStrategy(strategy: QuickSortStrategy())
let sortedQuick = bubbleSorter.sortList(list: myList)
print("Quick Sort: \(sortedQuick)")