Object-Oriented vs. Functional Programming

Chapter 2. SOLID Principles

Lambda-Enabled SOLID Principles

The SOLID principles are a set of basic principles for designing OO programs. The name itself is an acronym, with each of the five principles named after one of the letters: Single responsibility, Open/closed, Liskov substitution, Interface segregation, and Dependency inversion. The principles act as a set of guidelines to help you implement code that is easy to maintain and extend over time.

Each of the principles corresponds to a set of potential code smells that can exist in your code, and they offer a route out of the problems caused. Many books have been written on this topic, and I’m not going to cover the principles in comprehensive detail.

In the case of all these object-oriented principles, I’ve tried to find a conceptually related approach from the functional-programming realm. The goal here is to both show functional and object-oriented programming are related, and also what object-oriented programmers can learn from a functional style.

The Single-Responsibility Principle

Every class or method in your program should have only a single reason to change.

An inevitable fact of software development is that requirements change over time. Whether because a new feature needs to be added, your understanding of your problem domain or customer has changed, or you need your application to be faster, over time software must evolve.

When the requirements of your software change, the responsibilities of the classes and ...