With the help of OOP fundamentals and design patterns, application development was divided into groups of functionalities. OOP protocols made many things easy and useful, such as introducing an interface with which we can implement loosely-coupled designs, encapsulation with which we can hide object data, and inheritance-extending functionalities, by classes, with which we can reuse work.

These advantages of OOP also add complexity as the system grows. With added complexities, the cost to maintain it and the chances of failure increase. To solve this, modularizing functionalities into simpler and more manageable modules helps reduce complexity.

To modularize a system, we started following a practice of dividing applications into different logical layers, for example, presentation layer, service layer, and data layer. However, even after dividing the functionalities into different layers, there are certain functionalities that are required in all layers, for example, security, logging, caching, and performance monitoring. These functionalities are called crosscutting concerns.

If we implement these crosscutting concerns using inheritance, it will violate the single responsibility of the SOLID principle and increase the object hierarchy. And if we implement them using composition, it will be more complicated. So the implementation of crosscutting concerns using OOP leads to two problems:

• Code tangling
• Code scattering

Let's discuss these problems more.