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Guide to Open Closed Principle in Swift

Guide to Open Closed Principle  in Swift

The Open Closed Principle (OCP) is one of the SOLID principles of object-oriented design. This principle advocates that software entities should be open for extension but closed for modification. In simpler terms, once a class is implemented, it should remain unchanged while still allowing new functionality to be added. This article delves into the Open-Closed Principle, exploring its significance in Swift development and showcasing practical examples.

The Open Closed Principle is one of the SOLID principles, promoting code maintainability, scalability, and extensibility. It encourages engineers to design classes and modules in a way that new features or behavior can be added without altering the existing codebase. This ensures that changes don't introduce new bugs or disrupt existing functionality.

In the context of Swift development, the Open Closed Principle translates to creating code that can be extended with new features using protocols, inheritance, and abstractions. By adhering to this principle, you minimize the risk of breaking existing code when introducing new functionality.


Shape Drawing

Consider an example where you're building an app that draws various shapes. Instead of creating a monolithic class that handles all shapes, you can follow the Open Closed Principle:

protocol Shape {
    func draw()

class Circle: Shape {
    func draw() {
        // Draw circle

class Square: Shape {
    func draw() {
        // Draw square

// Additional shape classes can be added without modifying existing code
class Triangle: Shape {
    func draw() {
        // Draw triangle

In this scenario, new shapes can be added without updating the existing Shape protocol or the implementation of other shape classes. This is how the Open-Closed Principle do by extending the application's functionality while keeping existing code untouched.

Benefits of Open Closed Principle

  • Maintainability: Existing code remains stable, reducing the chances of introducing bugs while extending functionality.
  • Scalability: New features can be added with ease.
  • Collaboration: Different teams can work on extending functionality without interfering with each other's work.

Challenges and Considerations

While embracing the Open Closed Principle, it's crucial to strike a balance. Overzealous adherence might lead to overly complex abstractions. It's essential to identify stable parts of the system that are less likely to change and design them accordingly, while allowing flexible extension points for volatile components.


The Open Closed Principle is a guiding light in software design, advocating a balance between maintaining existing code and extending functionality. In Swift development, adhering to this principle fosters code that is both resilient and adaptable.