#2 SOLID - Open Close Principle | Swift | iOS Development

It states that software entities (classes, modules, functions, etc.)
should be open for extension but closed for modification.

• In the below example, the Shape class violates the Open-Closed Principle because it is not closed for modification ❌.
• Whenever a new shape is added (e.g., triangle, rectangle), the Shape class needs to be modified to include a new case in the ShapeType enum and update the area() method accordingly.
• This violates the principle as the class is not closed for modification.

enum ShapeType {
    case circle
    case square
}

class Shape {
    var type: ShapeType

    init(type: ShapeType) {
        self.type = type
    }

    func area() -> Double {
        switch type {
        case .circle:
            // Calculate circle area
            return 3.14 * 5 * 5
        case .square:
            // Calculate square area
            return 10 * 10
        }
    }
}

let shapes: [Shape] = [Shape(type: .circle), Shape(type: .square)]

• In the below example, the Open-Closed Principle is applied correctly ✅.
• The Shape protocol defines the contract for shapes, and different shapes (e.g., Circle and Square) implement the Shape protocol and provide their own implementation of the area() method.
• Now, if you want to add a new shape (e.g., Triangle), you can simply create a new struct conforming to the Shape protocol without modifying any existing code.
• This adheres to the Open-Closed Principle as the code is closed for modification but open for extension.

enum ShapeType {
    case circle
    case square
}

protocol Shape {
    func area() -> Double
}

struct Circle: Shape {
    func area() -> Double {
        // Calculate circle area
        return 3.14 * 5 * 5
    }
}

struct Square: Shape {
    func area() -> Double {
        // Calculate square area
        return 10 * 10
    }
}

let shapes: [Shape] = [Circle(), Square()]