The Robert C. Martin Clean Code Collection (Collection) (Robert C. Martin Series)

by Robert C. Martin

Just the act of breaking large functions into smaller functions causes a proliferation of classes. Consider a large function with many variables declared within it. Let’s say you want to extract one small part of that function into a separate function. However, the code you want to extract uses four of the variables declared in the function. Must you pass all four of those variables into the new function as arguments? Not at all! If we promoted those four variables to instance variables of the class, then we could extract the code without passing any variables at all. It would be easy to break the function up into small pieces. Unfortunately, this also means that our classes lose cohesion because they accumulate more and more instance variables that exist solely to allow a few functions to share them. But wait! If there are a few functions that want to share certain variables, doesn’t that make them a class in their own right? Of course it does. When classes lose cohesion, split them! So breaking a large function into many smaller functions often gives us the opportunity to split several smaller classes out as well. This gives our program a much better organization and a more transparent structure.