Evocative Development
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Mehdi Bizhani
SOLID Principles
## SOLID Principles === ### Principles | | | |-------|---------------------------| | **S** | Single Responsibility | | **O** | Open/Closed (OCP) | | **L** | Liskov Substitution (LSP) | | **I** | Interface Segregation | | **D** | Dependency Inversion | === ### Single Responsibility - A class should only have one responsibility - Only one reason to change - Advantages - Testing - fewer test cases - Lower Coupling - fewer dependencies === ### Open/Closed (OCP) - Classes - Open for extension - Closed for modification - Solutions - `inheritance` as a mechanism to inherit existing code, and add extra functionality in the subclass - `decorator design pattern` by applying composition on existing code, and add extra functionality in the `wrapper` class === ### Liskov Substitution (LSP) <table> <tr> <td colspan="2" style="border:0"> <ul> <li> If class <code>Child</code> is a subtype of class <code>Parent</code>, it should be possible to replace <code>Parent</code> with any <code>Child</code> without disrupting the behavior of the program. </li> <li> If <code>test(Parent)</code> passed => both <code>test(Child1)</code> and <code>test(Child2)</code> should pass! </li> </ul> </td> </tr> <tr> <td> <ul> <li>It ensures conformity in all classes in the entire hierarchy.</li> </ul> </td> <td> <img width="1000" src="/assets/images/slides/solid/liskov-class-diagram.png" /> </td> </tr> </table> --- #### Sample  === ### Interface Segregation - Larger interfaces should be split into smaller ones - Implementing classes only need to be concerned about the methods that are of interest to them === ### Dependency Inversion - For decoupling of software modules, both high-level and low-level modules should depend on abstractions: - High-level modules/classes should not depend on low-level modules/classes. Both should depend upon abstractions. - Abstractions should not depend upon details. Details should depend upon abstractions. - Different from `dependency injection` === ### References - [A Solid Guide to SOLID Principles](https://www.baeldung.com/solid-principles) - [The Liskov Substitution Principle (LSP)](https://www.linkedin.com/pulse/liskov-substitution-principle-lsp-paul-gichure-ctfl/) - [SOLID Principle in Programming: Understand With Real Life Examples](https://www.geeksforgeeks.org/solid-principle-in-programming-understand-with-real-life-examples/)