In this chapter, we're not focusing on the architecture and tools required to manage a solution's life cycle (sometimes called the development ecosystem) but on the quality of the code and its structures in terms of efficacy, precision, and maintainability.
We'll start with the SOLID principles, proposed by Robert Martin, which are gaining more and more recognition and that we can see implemented in different frameworks and technologies.
A basic application will be used to illustrate the distinct principles, and as the requirements evolve, we'll apply different principles and patterns to solve the problems.
Finally, we'll go through the eight most used patterns of the Gang of Four (according to statistics), revising its definitions and purpose to finish with the current list of available patterns created and published after the GoF group published their book.
Therefore, the topics covered in this chapter are as follows:
- SOLID principles
- Open/Closed principle
- Liskov Substitution principle
- Interface Segregation principle
- Dependency Inversion principle
- Design patterns
- Other software patterns
- Other patterns
With time, programming techniques have evolved, at the same pace as languages and hardware; so, from the initial confusion in the early 60s, when no foundations were established and few models were considered, the 70s marked the start of the adoption of other paradigms, such as procedural programming, and later on, object oriented programming (OOP).
Ole-Johan Dahl and Kristen Nygaard originally proposed OOP with the Simula language, when they both worked at the Norwegian Computing Center. They were given the Turing Award for these achievements, among other recognitions.
A few years later (around 1979), Bjarne Stroustrup created C with Classes, the prototype of what C++ today is because he found valuable aspects in Simula, but he thought that it was too slow for practical purposes. C++ originally had imperative features and object-oriented and generic ones, while also providing the ability to program for low-level memory manipulation.
It was the first OOP language that became universal in adoption (though limited in number), due to its many virtues, but for many people, it was not adequate for business applications.
Later on, the appearance of Java and the .NET platforms proposed a much easier and affordable solution for many programmers while still moving within the ordered space that object oriented programming languages promote.
So, OOP was adopted, and up until this date, no other important programming paradigm has substituted these ideas. Surely, there are other approaches, such as functional programming, but even the most significant representative of this tendency, JavaScript, is becoming more object-oriented in the latest versions (ECMAScript 2015).
With the accelerated expansion of software solutions, many lessons were learned about how to correctly afford common software problems, and that will be our starting point.