🧩 SOLID & Patterns: The Ultimate Code Harmony Guide (2026)

Coding design patterns are the practical blueprints that bring SOLID principles to life. While SOLID provides the philosophical “why” for clean architecture, design patterns offer the concrete “how” to achieve it. If you’ve ever wondered how do coding design patterns relate to SOLID principles, the answer is simple: patterns are the tools we use to enforce these rules in real-world code.

Imagine trying to build a skyscraper with only a list of safety regulations but no architectural drawings. That’s what coding without design patterns feels like when you try to follow SOLID. You know what you need to avoid (like a “God Object”), but you lack the proven structure to build it correctly.

We once watched a team refactor a 2,0-line “spaghetti” class into 40 tiny, testable files. They didn’t just split the code; they applied the Strategy Pattern to honor the Single Responsibility Principle. The result? A codebase that could be updated in hours instead of days.

Key Takeaways

  • SOLID is the Compass, Patterns are the Map: SOLID principles define the goals of maintainable code, while design patterns provide the specific implementations to reach those goals.
  • Interdependence is Key: You cannot effectively apply patterns like Dependency Injection or Strategy without adhering to principles like Dependency Inversion and Single Responsibility.
  • Universal Application: These relationships hold true across paradigms, from Object-Oriented C# and Java to Functional Haskell and Elixir.
  • Avoid Over-Engineering: Use patterns only when they solve a specific SOLID violation; forcing a pattern where it doesn’t fit creates unnecessary complexity.

Table of Contents

⚡️ Quick Tips and Facts

Before we dive into the deep end of the architectural ocean, let’s grab a life preserver. Here are some hard truths and golden nugets about the relationship between SOLID principles and coding design patterns that every developer should know:

  • SOLID is the “Why,” Patterns are the “How”: Think of SOLID as the constitution of your codebase and design patterns as the specific laws enacted to uphold that constitution. You can’t really have a robust pattern without the guiding philosophy of SOLID.
  • The “God Object” is the Enemy: If a single class is trying to handle database connections, user authentication, and email notifications simultaneously, it’s violating the Single Responsibility Principle (SRP). This is the #1 cause of “spaghetti code.”
  • Patterns aren’t Magic Spells: Applying the Factory Pattern won’t fix bad architecture if you ignore the Dependency Inversion Principle (DIP). It’s like putting a Ferrari engine in a tractor; it might go fast, but it’ll fall apart.
  • Functional Programming (FP) isn’t Exempt: Even if you’re writing in Haskell or Elixir, the intent of SOLID remains. As noted by experts like Patricio Ferraggi, if your function has only one reason to change, you are applying SRP, regardless of whether you use classes or pure functions.
  • Over-Engineering is Real: Just because you can use the Observer Pattern doesn’t mean you should. Sometimes a simple if/else block is the most SOLID solution for a specific context.

For a deeper dive into the mechanics of these structures, check out our comprehensive guide on coding design patterns.

📜 The Genesis: How SOLID Principles Shaped Modern Design Patterns


Video: 5 Design Patterns That Are ACTUALLY Used By Developers.








Let’s take a trip back to the early 20s. The software world was a chaotic mess of “copy-paste” programming. Classes were bloated, inheritance hierarchies were fragile, and changing one line of code often broke three other features. Enter Robert C. Martin (Uncle Bob), who codified five principles that would become the bedrock of modern object-oriented design.

But here’s the twist: SOLID didn’t invent design patterns; it gave them a purpose.

Before SOLID, patterns like the Strategy Pattern or Decorator Pattern were just clever tricks. After SOLID, they became architectural necessities. The principles provided the rationale for why we structure code the way we do.

“As long as your function or class or module has only one reason to change then you are applying this principle.” — Patricio Ferraggi

This quote highlights a crucial insight: SOLID isn’t about syntax; it’s about change management. Design patterns are the tools we use to manage that change effectively.

The Evolution of Thought

  • Pre-SOLID Era: Code was rigid. Adding a new payment method meant opening the Order class and adding a giant switch statement.
  • Post-SOLID Era: We use the Open/Closed Principle (OCP) to extend behavior without touching existing code, often utilizing the Strategy Pattern.

This shift transformed software development from a craft of “making it work” to an engineering discipline of “making it last.”

🧩 The Grand Dance: Mapping SOLID Principles to Specific Design Patterns


Video: 10 Design Patterns Explained in 10 Minutes.








Now, let’s get our hands dirty. How exactly do these five principles map to the 23 Gang of Four (GoF) patterns? We’ve broken it down into a definitive guide that connects the abstract philosophy to concrete implementation.

1. Single Responsibility Principle (SRP) and the Strategy & Factory Patterns

SRP states: A class should have one, and only one, reason to change.

Imagine you’re building a game for Unity. You have a Player class that handles movement, health, inventory, and saving to the disk. If the save format changes, you have touch the Player class. If the movement physics change, you touch it again. That’s a recipe for disaster.

The Solution:

  • Strategy Pattern: Instead of hardcoding movement logic, we extract it into a MovementStrategy interface. Now, changing how the player moves doesn’t affect the Player class’s core logic.
  • Factory Pattern: We use a factory to create different types of Player instances based on specific configurations, ensuring the creation logic isolated from the usage logic.
Pattern SOLID Connection Real-World Analogy
Strategy SRP A chef (class) doesn’t need to know how to chop, sautĂ©, or bake; they just follow a recipe (strategy) provided by a sous-chef.
Factory SRP A car dealership (factory) handles the complex process of building cars, so the customer (client) just picks a model.

Pro Tip: If a class name requires the word “and” (e.g., UserManagerAndEmailSender), it’s likely violating SRP. Split it!

2. Open/Closed Principle (OCP) and the Template Method & Decorator Patterns

OCP states: Software entities should be open for extension, but closed for modification.

This is the holy grail of maintainability. You want to add features without breaking existing unit tests.

The Solution:

  • Template Method Pattern: Define the skeleton of an algorithm in a base class, letting subclasses override specific steps. You don’t change the base class; you just add a new subclass.
  • Decorator Pattern: Add behavior to objects dynamically by wrapping them. Need to add logging to a FileReader? Wrap it in a LoggingFileReader. The original FileReader remains untouched.

“Open to extension but closed to modification.” — Common Video Insight

In app development, this is crucial. Imagine you’re building a payment system. You have CreditCardProcessor. A new client wants CryptoProcessor. With OCP, you don’t rewrite the payment logic; you just create a new processor class that adheres to the PaymentInterface.

3. Liskov Substitution Principle (LSP) and the Adapter & Bridge Patterns

LSP states: Subclasses must be substitutable for their base classes without breaking the application.

This is where many developers trip up. Just because a class looks like it should inherit from another doesn’t mean it should.

The Solution:

  • Adapter Pattern: If you have a legacy class that doesn’t fit your new interface, use an adapter to make it work without forcing a broken inheritance hierarchy.
  • Bridge Pattern: Decouple an abstraction from its implementation so they can vary independently. This prevents the “fragile base class” problem where changing the base breaks all children.

Real-World Example:
If you have a Bird class with a fly() method, and you create a Penguin class that inherits from Bird, you violate LSP because penguins can’t fly. The fix? Create a FlyingBird and a SwimmingBird class, or use composition.

4. Interface Segregation Principle (ISP) and the Facade & Proxy Patterns

ISP states: Clients should not be forced to depend on interfaces they do not use.

Nobody likes a “fat interface.” If you have an interface with 20 methods, but your client only needs 2, you’re violating ISP.

The Solution:

  • Facade Pattern: Provide a simplified interface to a complex subsystem. The client doesn’t need to know about the 50 internal classes; they just talk to the Facade.
  • Proxy Pattern: Control access to an object. If a client only needs to read data, give them a read-only proxy, not the full object with write capabilities.

Why it matters: In Back-End Technologies, this reduces coupling. If the Write interface changes, the Read client doesn’t care.

5. Dependency Inversion Principle (DIP) and the Dependency Injection Pattern

DIP states: High-level modules should not depend on low-level modules. Both should depend on abstractions.

This is the principle that makes unit testing possible. If your OrderService creates a DatabaseConnection directly, you can’t test OrderService without a real database.

The Solution:

  • Dependency Injection (DI): Pass the DatabaseConnection (or rather, an interface IDatabase) into the OrderService via the constructor. Now you can inject a MockDatabase during testing.

“High-level modules shouldn’t depend on low-level modules. They should both depend on an abstraction.” — Common Video Insight

This is the backbone of modern frameworks like Spring (Java) and ASP.NET Core.

🚫 When Patterns Clash: Navigating Conflicts Between SOLID and Real-World Code


Video: Software Design – Introduction to SOLID Principles in 8 Minutes.








Here’s the dirty secret: SOLID principles sometimes fight each other.

Imagine you need to implement the SRP (one class, one job) and the ISP (small interfaces). You end up with hundreds of tiny classes and interfaces. Suddenly, your codebase is a maze of indirection. This is known as “Patternitis” or over-enginering.

The Conflict:

  • SRP pushes you to split everything.
  • OCP pushes you to create new classes for every variation.
  • Result: A codebase that is technically “SOLID” but impossible to navigate.

The Resolution:
Balance is key. As the video summary suggests, the ultimate goal is to keep code as simple as possible. Sometimes, a little bit of “impurity” is better than a perfect architecture that no one understands.

We’ve seen teams refactor a simple 50-line script into 50 files, each with 10 lines of code, just to satisfy a linter. Don’t be that team.

🧪 Beyond the Basics: SOLID in Functional Programming vs. Object-Oriented Paradigms


Video: Master Design Patterns & SOLID Principles in C# – Full OOP Course for Beginners.







You might be thinking, “But I use Functional Programming (FP)! I don’t have classes, so SOLID doesn’t apply, right?”

Wrong.

As discussed in the article by Patricio Ferraggi, SOLID is about intent, not syntax.

Principle OP Implementation FP Implementation
SRP One class, one job. One function, one job.
OCP Inheritance & Polymorphism. Composition & Higher-Order Functions.
LSP Subclass substitutability. Parametric polymorphism (Generics).
ISP Small interfaces. Small, specific function signatures.
DIP Dependency Injection. Passing functions as arguments.

In FP, composition replaces inheritance. Instead of extending a class, you compose small, pure functions to create complex behavior. This naturally adheres to OCP because you aren’t modifying existing code; you’re building new behaviors from existing ones.

Key Insight: Whether you’re using C#, Java, Haskell, or Elixir, the goal remains the same: minimize the impact of change.

🛠️ Practical Refactoring: Turning “Spaghetti Code” into SOLID Architecture


Video: Design patterns are for brainless programmers • Mike Acton.







Let’s walk through a real-world scenario. You inherit a legacy game development project in Unity. The GameManager class is 2,0 lines long. It handles input, physics, UI, saving, and networking.

Step 1: Identify the Violations

  • SRP: It does everything.
  • DIP: It creates NetworkManager and SaveManager directly inside its methods.

Step 2: Extract Responsibilities

  • Create InputHandler, PhysicsController, UIManager, SaveService, and NetworkService.
  • Apply SRP to each.

Step 3: Apply Interfaces

  • Define ISaveService and INetworkService.
  • Refactor GameManager to depend on these interfaces, not the concrete classes.

Step 4: Inject Dependencies

  • Use a Dependency Injection container (like Zenject in Unity) to wire everything up.

Result:
Now, if you want to change the save format, you only touch SaveService. If you want to switch from TCP to UDP, you only touch NetworkService. The GameManager remains stable.

🤔 Common Pitfalls: Over-Engineering and the “Patternitis” Trap


Video: SOLID Design Principles with Java Examples | Clean Code and Best Practices | Geekific.








We’ve all been there. You see a pattern, and you think, “I must use this!”

The Trap:

  • Using the Observer Pattern for a simple event that only happens once.
  • Creating an interface for a class that will never have more than one implementation.
  • Applying DIP when the low-level module is stable and unlikely to change.

The Fix:
Ask yourself: “Will this change?”
If the answer is no, don’t over-enginer it. Simplicity is the ultimate sophistication.

“A class should only really have one reason to change.” — Common Video Insight

If you can’t identify a reason for change, maybe you don’t need a pattern yet.

🏆 Case Studies: How Top Tech Giants Leverage SOLID and Patterns


Video: What Are SOLID Principles?








Let’s look at how the pros do it.

Netflix

Netflix uses microservices heavily. Each service adheres to SRP (one service does one thing). They use API Gateways (a form of Facade Pattern) to route requests. This allows them to update the “Recommendation Service” without touching the “Streaming Service.”

Microsoft (ASP.NET Core)

The entire framework is built on DIP. Controllers depend on interfaces, not concrete implementations. This allows for easy Dependency Injection and robust unit testing.

Unity Technologies

Unity’s component system is a practical application of Composition over Inheritance. Instead of deep inheritance trees, game objects are composed of MonoBehaviour components, each handling a specific responsibility (SRP).

🧠 Quick Tips and Facts (Recap)

Just to drive it home:

  • SOLID is your compass; Patterns are your map.
  • SRP prevents the “God Object.”
  • OCP saves you from rewriting code.
  • LSP ensures your hierarchy makes sense.
  • ISP keeps interfaces lean.
  • DIP makes testing a breeze.

Remember, these aren’t rules written in stone; they are guidelines to help you write code that is maintainable, scalable, and understandable.

Conclusion

a diagram of a number of circles and a number of dots

So, how do coding design patterns relate to SOLID principles? The answer is simple yet profound: Design patterns are the practical application of SOLID principles.

SOLID provides the philosophical framework for writing clean, maintainable code. It tells us why we should structure our code a certain way. Design patterns provide the blueprints for how to achieve that structure. You cannot have effective design patterns without the guiding light of SOLID, and SOLID principles often remain abstract without the concrete examples provided by patterns.

We started this journey by asking if SOLID applies to Functional Programming. The answer is a resounding yes. Whether you are using classes in C# or pure functions in Haskell, the core intent of SOLID—managing change and reducing coupling—remains the same.

Our Recommendation:
Don’t treat SOLID as a checklist to be rigidly followed. Treat it as a mindset. When you encounter a problem, ask:

  1. Does this class have one reason to change? (SRP)
  2. Can I add this feature without modifying existing code? (OCP)
  3. Can I swap this component without breaking things? (LSP)
  4. Is this interface too bloated? (ISP)
  5. Am I depending on concrete implementations? (DIP)

If you can answer “yes” to these, you are on the right path. And if you find yourself over-enginering, remember: Simplicity wins.

For those looking to deepen their understanding, we highly recommend exploring the Dependency Injection patterns in modern frameworks and studying the Strategy Pattern for flexible algorithm design.

Want to level up your coding game? Here are some resources we trust:

Books & Resources:

Tools & Frameworks:

Internal Guides:

FAQ

a black and white photo of a large object

How do SOLID principles improve code maintainability in game development?

H3: How do SOLID principles improve code maintainability in game development?
In game development, requirements change rapidly. A mechanic that works today might need a complete overhaul tomorrow. SRP ensures that if you need to change the physics of a character, you don’t accidentally break their inventory system. OCP allows you to add new weapon types without rewriting the combat logic. DIP lets you swap out the audio engine or rendering backend without touching the core game loop. This modularity is essential for long-term project health.

Read more about “🎮 8 Real-World Design Patterns Powering Your Favorite Games (2026)”

Which design patterns best support the Single Responsibility Principle?

H3: Which design patterns best support the Single Responsibility Principle?
The Strategy Pattern is the champion of SRP. It allows you to extract different algorithms into separate classes, ensuring each class has only one reason to change. The Factory Pattern also supports SRP by isolating object creation logic from object usage logic. Additionally, the Command Pattern encapsulates requests as objects, separating the execution logic from the invocation logic.

Can you implement Dependency Inversion without using design patterns?

H3: Can you implement Dependency Inversion without using design patterns?
Absolutely. Dependency Inversion is a principle, not a pattern. You can achieve it simply by defining an interface and passing an implementation of that interface into a class via its constructor. While Dependency Injection is the most common pattern used to implement DIP, you can manually pass dependencies without a formal DI container or complex pattern structure. The key is the abstraction, not the mechanism.

Read more about “🚫 7 Deadly Anti-Patterns to Avoid When Using Design Patterns (2026)”

How do design patterns help adhere to the Open/Closed Principle in app development?

H3: How do design patterns help adhere to the Open/Closed Principle in app development?
Design patterns like the Decorator Pattern and Template Method Pattern are specifically designed to support OCP. The Decorator Pattern allows you to add new features to an object dynamically by wrapping it, avoiding the need to modify the original class. The Template Method Pattern defines the skeleton of an algorithm, allowing subclasses to override specific steps without changing the overall structure.

Read more about “🏗️ Creational vs. Structural vs. Behavioral: The Ultimate Design Pattern Showdown (2026)”

What is the relationship between the Strategy pattern and the Interface Segregation Principle?

H3: What is the relationship between the Strategy pattern and the Interface Segregation Principle?
The Strategy Pattern relies heavily on ISP. In the Strategy pattern, you define a small, specific interface (e.g., ISortStrategy) that only contains the method needed for the strategy (e.g., sort()). This prevents clients from being forced to implement methods they don’t use. If the interface were bloated with unrelated methods, it would violate ISP and make the pattern harder to implement.

Do SOLID principles limit the use of common design patterns in mobile apps?

H3: Do SOLID principles limit the use of common design patterns in mobile apps?
Not at all. In fact, SOLID principles enable the use of design patterns in mobile apps by ensuring they are implemented correctly. Mobile apps often have limited resources and frequent updates. Adhering to SRP and OCP ensures that app features can be updated or removed without crashing the entire application. However, blindly applying patterns without considering the context can lead to over-enginering, which is a risk in resource-constrained environments.

How can Liskov Substitution Principle guide the choice of design patterns in object-oriented games?

H3: How can Liskov Substitution Principle guide the choice of design patterns in object-oriented games?
LSP is critical when choosing inheritance-based patterns like the Template Method or Factory patterns. If you are designing a hierarchy of game entities (e.g., Enemy, Boss, Minion), LSP ensures that a Boss can be used anywhere an Enemy is expected without breaking the game logic. If a Boss has a unique behavior that breaks the Enemy contract, LSP suggests you should refactor the hierarchy, perhaps by introducing a more general Character class or using composition instead of inheritance.

Jacob
Jacob

Jacob is a software engineer with over 2 decades of experience in the field. His experience ranges from working in fortune 500 retailers, to software startups as diverse as the the medical or gaming industries. He has full stack experience and has even developed a number of successful mobile apps and games. His latest passion is AI and machine learning.

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