How can you improve your code quality with SOLID principles?

The SOLID principles are indeed fundamental principles of software design that aim to improve the maintainability and flexibility of code. They provide guidelines for creating clean, modular, and maintainable software. I totally believe all design solutions and patterns are exist to inspire us how to use the SOLID principles and the software knowledge to solve problems and to secure your architecture.

SOLID doesn't answer every question, and knowing it doesn't automatically make you a good software architect. However, it is a reliable foundation from which to start. Time and again, I find myself going back to these principles to help me write code. Also, many issues I see in code can be framed in the context of how that issue was caused as a result of violating one of these principles.

The SOLID principles are guidelines, not rules. They are meant to be used as a general framework for creating good object-oriented designs. There may be times when it is not possible to follow all of the principles, but following as many of them as possible will help to create code that is more maintainable, flexible, and extensible. Ultimately, the decision of whether or not to follow the SOLID principles is up to the individual developer or team. However, following these principles can help to create code that is more maintainable, flexible, and extensible.

These principles are hardly new or groundbreaking. I've been a coder since the early 90's and these were all common practices that we all followed. What is truly distressing is that there is no emphasis on writing resilient code - that is, code that not only handles errors but attempts to recover from them and continue execution - or at least generate a meaningful log message. Too many times I have reviewed "happy path" code, where every login in expected to work, every file opens, DNS always works, remote services never time out - with only vague log messages stating that an error occurred.

Incorporating SOLID principles into your coding routine is akin to hiring a skilled architect before building a house. Just as an architect ensures the house's foundation is strong, rooms are purposefully designed, and future modifications won't require tearing down walls, the SOLID principles guide you in crafting code that's robust and adaptable. This shift in approach transformed how I view software development, making me realize that spending more time thinking about design upfront saves countless hours of refactoring later. Code following these principles, like a well-designed building, stands the test of time and adapts gracefully to new requirements.

The trick with single responsibility principle is to make sure you determine a reasonable granularity for what is considered a responsibility, so that you don't overengineer. Otherwise, this principle is pretty fundamental to good software design.

Adhering to the Single Responsibility Principle (SRP) in software design involves ensuring that each class or module has a clear, singular purpose, reducing the potential reasons for it to change. This is achieved by separating different concerns into distinct classes, avoiding the mixing of input/output operations with core logic, and favoring composition over cramming multiple responsibilities into one class. Regular refactoring, meaningful documentation, and naming conventions are essential. Also, keeping classes small, fostering a culture of code reviews, and following the SOLID principles contribute to creating more maintainable and adaptable software systems.

The most underrated principle is the single responsibility principle. The SRP helps to avoid ripple effects by ensuring that each class is responsible for a single, well-defined task. This makes it easier to understand and change the code, and it reduces the chances of making changes that have unintended consequences.

Single responsibility is an approach based entirely on the concept of “Do one thing, do it well”. This is also the Unix philosophy and is part of clean coding.

Once you identify classes with too many responsibilities, use the Single Responsibility principle as a refactoring technique to create smaller classes with single responsibilities and focus only on one business actor.

When you think about the OCP, you can always think about the interfaces, which can have different implementations in each concert class. For the example mentioned here, you can have an interface and implement it in the classes that need to have the calculatePrice function, Take a look at the code: Interface Priceable { public function CalculatePrice(); } Class ProductOne implements Pricable { public function CalculatePrice() { // the concrete implementation. } }

A class should be open to extensions but closed to code changes. So, if we want to add a new feature to our existing application, we must solve the problem with a new class or classes without making any changes to the existing application codes.

Whilst the conventional wisdom of OCP advocates the use of inheritance to make code extensible, I would advocate to limit how much you rely on inheritance. Deep inheritance hierarchies become difficult to maintain, and objects at the end of the inheritance chain end up suffering the same problems as implementations of large interfaces. The key for extensibility is polymorphism - specifically the use of abstractions - and the composition of objects out of many interfaces.

In my experience with mobile applications, if we have methods for communicating with the server, we can extend them for new versions of the app without modifying the existing system. This ensures backward compatibility for the app.

The Open-Closed Principle (OCP) plays a pivotal role in software design by promoting code flexibility and maintainability. By adhering to this principle, developers can extend their software systems without the perilous task of altering existing, often well-tested code. This brings significant advantages, such as reducing the likelihood of introducing bugs when adding new features. One effective trick to uphold the OCP is employing polymorphism and inheritance. By creating specialized subclasses or using interfaces, developers can seamlessly introduce new functionality without tampering with the existing codebase. This practice not only keeps code clean and modular but also fosters a robust foundation for long-term software evolution.

The most easiest way to understand this principle is "Every child class should have use-case for each and every method of its parent class". Example : the parent class has two methods: A and B. The child class, X, can use method A, but it cannot use method B. This is a violation of the LSP because the child class is not substitutable for its parent class. To satisfy the LSP, the child class must be able to use all of the methods of its parent class. In this case, the child class would need to add a method that implements the functionality of method B.

Unit and Integration testing can help you here. When you will be writing the unit testing and mocking the dependencies there, you can start to notice if you are injecting concrete classes as dependencies. Integration testing also can help you when you mistakenly change the behavior of the code which will break your software functionality.

Again, try to stick to composition over inheritance. In this way you won't need to mess around child/parent relations a lot. But if you decided to use inheritance, then follow a simple rule: build children first following single responsibility principle, than extract common features into a common parent and make sure that you do not inherit a Figure class from Transform class. If that's the case, then switch to composition.

LSP and Interface Segregation Principle (ISP) are closely linked when it comes to interface design. For example, LSP emphasizes that implementations of an interface should be freely swappable without affecting the program's expected behavior. When classes have to implement interface methods they don't actually need, developers often stub out the method or have it throw an exception. This disrupts the expected behavior defined by the interface, thus violating LSP. In the case of an exception, client code is now forced to do a type-check to avoid it, which defeats the purpose of abstraction. The solution lies in understanding that this is also an ISP violation. In these cases, the interface is poorly designed and should be rewritten.

The Liskov Substitution Principle (LSP) is like ensuring all puzzle pieces fit perfectly, no matter where you place them. Any child class must be able to seamlessly take the place of its parent class. LSP tells us to design our classes to play nicely together, ensuring a square can always fit into the parent rectangle-shaped hole without forcing or breaking anything. It's about keeping promises with your code, ensuring everything works together smoothly.

In other words interface should describe one particular behavior that is common for set of types, interfaces typicaly answers the question "what one thing should my objects be able to do?", and if some type has multiple capabilities it should implement multiple interfaces, one for each capability. By the way here is the difference between interface and abstract class - abstract class usually describe the object itself and answers the question "what are my objects generally?".

The Interface Segregation Principle (ISP) states that clients should not be forced to depend on interfaces that they do not use. Lets assume example : The payment gateway interface has a method called sendOTP(). The 2DS payment gateway does not use this method, so it is being forced to depend on an interface that it does not use. This is a violation of the ISP. To satisfy the ISP, we should create separate interfaces for the methods that are actually used by each payment gateway. For example, we could create an interface for sending payments and an interface for sending OTPs. The 2DS payment gateway would then only need to implement the interface for sending payments.

In a way, this is a derivative of the Single Responsibility Principle. Programming to interfaces focused on a single responsibility allows for easier extensibility or replacement of underlying functionality. This translates to better adaptability of the software to different use case requirements.

Imagine that you need to implement an interface that contains 10 methods, Take 10 seconds and imagine that. Did you imagine how this can be painful? So always think about how to keep your interfaces smaller and business-related. This will make it easier for you when it comes to the implementation of your concrete class because you can choose which interfaces you need to implement in your concrete class.

An interface is a contract that defines the expected behaviour of all implementations. The more you add to this contract, the greater the burden on all implementations to fulfill it. Eventually, the interface gets bulky enough that initial design assumptions begin to break down and the implementations themselves become difficult to maintain. Interface Segregation Principle is here to tell us to keep interfaces small. Ideally, our objects should be composed of many small interfaces. If interfaces get too bulky, aim to split them out early on because that upfront refactoring cost will be much smaller than the refactoring cost you'll pay later if you let the interface get larger.

This is a really important principle. It will help you so much with the Domain Driven Design. Always consider the following: - The business logic should be separated, and it is not depending on any external dependencies (like ORM lib). - The external dependencies (ORM or Rabbitmq SDK) shouldn't be used directly in your application, have an abstraction through the interfaces. - Always remember that the software is always changing, so design it to be ready for the change.

Abstractions are the foundation upon which all good object-oriented programming prospers. The trick is to learn how to make good abstractions that don't leak implementation details. Another rule of DIP is that "abstractions should not depend on details, details should depend on abstractions". That is to say, you should avoid writing interfaces around a single use-case, lest you create an interface that depends on the code using it and therefore leaks details about its implementation (i.e., a leaky abstraction). However, it is also possible to overengineer by focusing too much on making reuseable interfaces. Aim for abstractions that balance between specificity to meet immediate needs and flexibility for future extensibility.

A good application of DIP is when the system has multiple persistency layers for the same entity. If your model implements DIP and can receive the repository as a parameter, your life will be much easier.

A practical good advice for all of the principles is not to start with a lot of interfaces immediately. Instead of defining a full interface for the first go start with a few lambdas, in other words start with a few concrete function signatures. As you refactor you can asses which of these functions belong together under the same roof.

Practical Example `Report` class depends on a `DB` class to fetch data. Instead of directly calling methods from `DB` within `Report`, define an interface called `IDataFetcher`. --- public interface IDataFetcher { List<Data> FetchData(); } --- Both `Report` and `DB` classes will depend on this `IDataFetcher` interface. --- public class Report { private readonly IDataFetcher _dataFetcher; public Report(IDataFetcher dataFetcher) { _dataFetcher = dataFetcher; } public string GenerateReport() { var data = _dataFetcher.FetchData(); //return report } public class DB : IDataFetcher { public List<Data> FetchData() { // Fetch data... } }

Remember that these principles do not stand alone or in contrast to each other. Rather, they are complimentary and reinforce each other. Dependency Inversion Principle's advocation of abstractions only works as well as your abstractions are small and well-defined, as Interface Segregation Principle would have you make them. This, in turn, reinforces Liskov Substitution Principle, and ensures it is easier for you to maintain easily-swappable implementations. With these flexible abstractions and implementations, you reinforce Open/Closed Principle and Single Responsibility Principle by having code that is now easy to extend and easy to ultimately maintain.

To get the most out of the SOLID principles, consider how to incorporate them into the software development process. If you merely educate them, it is very simple to forget about them when you are focused on finishing the project and under time constraints. Consider how to include SOLID principles throughout each step, from software design to quality assurance.

I used to work at a place where we asked in interviews: "What are the SOLID principles?". Candidates would come prepared and reel off the Wikipedia definition. But we found that there's a difference between knowing the SOLID principles and understanding them. I knew the SOLID principles before I truly understood them. I learned to understand through practising Test Driven Development. Whilst TDD doesn't force the application of SOLID principles, being effective at TDD really encourages you to apply the principles. I would say applying the SOLID principles was probably the single most effective change I made that had the biggest impact on the quality of my code. That and TDD...

I use these principles as tools to reduce coupling and improve reusability. Design patterns are also very interesting. However it is important to look for compromise to avoid over-engineering.

I agree with Ivayo L. Mere paper based principles, templates and checklists are no longer sufficient. Now a days we need "Apps" that deliver executable artifacts for direct use in the programs / code being developed. The focus of new software development is "how to select and configure available sofrware components" and "develop only the minimum essential new software", which inturn can be added to the Reusable Software Artifacts Repository. ReSAR.