Liskov Substitution: The Real Meaning of Inheritance
After exploring Dependency Inversion and Interface Segregation, let’s tackle perhaps the most misunderstood principle of SOLID: The Liskov Substitution Principle (LSP).
Again, kudos to Uncle Bob for reminding me about the importance of good software architecture in his classic Clean Architecture! That book is my primary inspiration for this series. Without clean architecture, we’ll all be building firmware (my paraphrased summary).
The Liskov Substitution Principle states that if S is a subtype of T, then objects of type T may be replaced with objects of type S without altering any of the desirable properties of the program.
The problem? While mathematically a square is a rectangle, in terms of behavior substitutability, it isn’t. The Square class violates LSP because it changes the behavior that clients of Rectangle expect.
Liskov Substitution Principle is about more than just inheritance - it’s about behavioral compatibility and meeting expectations. When followed properly, it leads to more reliable and maintainable code by ensuring that components are truly interchangeable.
