PHP 8.4 Course in Practice - What is SOLID

SOLID is an acronym for 5 design principles in object-oriented programming conceived by Robert C. Martin. The successive letters refer to the following principles:

• S - Single-Responsibility Principle (SRP)
• O - Open-closed Principle (OCP)
• L - Liskov Substitution Principle (LSP)
• I - Interface Segregation Principle (ISP)
• D - Dependency Inversion Principle (DIP)

Single-Responsibility Principle (SRP)

The Single-Responsibility Principle states that a class should have only one reason to change. In other words, a class should have only one responsibility or job. This principle helps keep classes focused and makes them easier to understand, test, and maintain.

Open-Closed Principle (OCP)

The Open-Closed Principle states that software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. This means you should be able to add new functionality without changing existing code.

Liskov Substitution Principle (LSP)

The Liskov Substitution Principle states that objects of a superclass should be replaceable with objects of a subclass without breaking the application. This principle ensures that inheritance is used correctly.

Interface Segregation Principle (ISP)

The Interface Segregation Principle states that no client should be forced to depend on methods it does not use. This principle encourages the creation of smaller, more focused interfaces rather than large, monolithic ones.

Dependency Inversion Principle (DIP)

The Dependency Inversion Principle states that high-level modules should not depend on low-level modules. Both should depend on abstractions. Additionally, abstractions should not depend on details; details should depend on abstractions.

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