How to create maintainable and scalable software systems? 🧩
Tags: architecture, design, designsystem, webdev
Published: 2023-10-25 12:00:00

Can you create a software system that is easier to maintain and scale?

Creating maintainable and scalable software systems is a key challenge many software developers face. One solution to this challenge is following certain design principles and patterns, such as the SOLID principles and Model-View-Controller (MVC).

Explore SOLID principles and the Model-View-Controller (MVC) to demonstrate how to design modular, flexible, and robust software systems with this newsletter. Using a game model example, understand each principle and pattern and confidently apply them in your projects.

Continue reading for a better understanding of how to create software systems that are maintainable and scalable. 

## **SOLID Principles**

SOLID helps you to avoid bad software design patterns, engineering mistakes or technical debts. With SOLID, you can make your code more readable, cleaner, and easier to understand.

Let's use a game as an example to explain each of these principles:

Suppose you are building a simple game where the player controls a character that can move around a 2D platform. Here's how you can apply the SOLID principles:

**(S)Single responsibility:** a class/module should have a single responsibility or reason to change. This principle helps to keep classes small and focused, making them easier to understand and maintain.

**Example:** a Player class might be responsible for handling just the movement and actions of the character.

You can create a separate class for each responsibility, such as a Player class for handling the movement and actions of the player character, rather than bundling unrelated tasks in one class like collision detection or sound effects.




**(O)Open-closed:** to add extensibility and avoid modifying existing code, classes should be designed to be open for extension but closed for modification. In this principle, new functionality can be added without altering the existing codebase. It also helps to prevent code rot by discouraging the modification of working code.

**Example:** you can add a new type of 'enemy' to the game.
Instead of modifying the existing Enemy class, you could create a new class that extends Enemy and adds the new behavior. This way, you can add new functionality without modifying the existing code.




**(L)Liskov substitution:** derived classes should be substitutable for their base classes. This principle helps to ensure that derived classes behave as expected when used in place of their base classes. It also makes it easier to refactor code without breaking existing functionality.

**Example:** a 'GameObject' class may represent any object in the game world. You could create a subclass called player that extends GameObject. Since the player is a subclass of GameObject, you should be able to use Player objects anywhere that GameObject objects are expected without causing any issues.


**(I)Interface segregation:** classes should not be forced to implement interfaces they do not use. This principle helps to keep interfaces small and focused, making them easier to understand and maintain.

**Example:** a SoundEffect class can play different sound effects in the game. 

You could create an interface called SoundPlayable that has a playSound method. Then, you could create separate classes for each type of sound effects, such as JumpSound, that implement the SoundPlayable interface. This way, you can avoid forcing clients to depend on methods they don't need.


**(D)Dependency inversion:** High-level modules should not depend on low-level modules. This principle helps to ensure that code is loosely coupled and easier to maintain. It also makes it easier to switch out components without breaking existing functionality.

**Example:** a GameManager class can manage the game's overall state. This class might depend on lower-level classes such as Player or Enemy. However, you can apply the 'Dependency inversion principle' by defining interfaces for these lower-level classes and having GameManager depend on those interfaces instead. This way, you can swap out different implementations of these interfaces without affecting GameManager.

## **Model View Controller (MVC) Pattern**

A software design pattern separates an application into three main components: the model, the view, and the controller. In addition to defining the roles of objects in an application, the MVC pattern also defines how objects should communicate with each other. This involves creating abstract boundaries between the three types of objects (model, view, and controller) to ensure they interact with objects of other types only across those boundaries.

Let's go into detail for our game example. Imagine your game also allows the player to collect coins. To create this game, you would need to separate the game logic into three components, as follows:


**(M)Model:** the model component would represent the data and logic of the game. It would be responsible for tracking the player character's location, the coins' positions, and the player's score. It would also implement the game rules, such as collision detection between the player and the coins and updating the score when a coin is collected.

**(V)View:** the view component would represent the game's user interface. It would be responsible for displaying the game world to the player, including the player's character, the coins, and the score. It would also handle user input, such as keyboard or mouse events, and send them to the controller for processing.

**(C)Controller:** the controller component would act as the intermediary between the model and view components. It would be responsible for processing user input and updating the model and view accordingly. For example, when the player presses the arrow keys to move the character, the controller updates the character's position in the model and then notifies the view to update the display of the game world.

You can create a more modular and maintainable codebase by separating the game logic into these three components. For example, if you wanted to change how the game world is displayed, you could modify the view component without affecting the model or controller. Similarly, you could modify the model component without affecting the view or controller to add a new game rule, such as a timer.

## **MVC pattern in Apple's and facebook's software system**

Many web development frameworks, including Ruby on Rails, Django, and Spring MVC, have widely adopted the MVC pattern. However, it has also been used in desktop GUI applications like [Apple's Cocoa framework](https://developer.apple.com/library/archive/documentation/General/Conceptual/DevPedia-CocoaCore/MVC.html).

Facebook's React framework uses the [Flux architecture](https://opensource.fb.com/) variant of the MVC pattern. Flux introduces the concept of a "store" to manage the application state, which is separate from the model. React components act as the view and controller, updating the store based on user input.

**Want to learn more?** 

Read the Book "Clean Architecture: A Craftsman's Guide to Software Structure and Design" by Robert C. Martin