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The Pathologies of Code Qualities

It's often easier to see code qualities by discussing examples of when the qualities aren't present. Let's look at five common code qualities: cohesion, coupling, redundancy, readability, and encapsulation.

  • Cohesion. Strongly cohesive classes are classes whose functions are all related to each other. Strongly cohesive methods are methods that do only one thing. The pathology of weak cohesion is classes or methods that do unrelated things. We've heard very weakly cohesive classes called "god objects" presumably because they are somewhat omniscient in that everything takes place in them.1
  • Proper coupling. Having well-defined relationships between objects makes them easier to understand and likely to inadvertently cause problems when changing code. The pathology of improper coupling is the occurrence of side effects—that is, unexpected errors due to making changes elsewhere.
  • No redundancy. No redundancy is difficult to achieve. The more redundancy you have, the more time it will take to make changes. As we discussed in Chapter 4, Shalloway's Law and Shalloway's Principle, no redundancy is virtually impossible to achieve—but at least you want to make it so you don't have to find the duplication. Essentially, the pathology of redundancy is that when you make a change in one place, you have to make a change in another place.
  • Readability. Readable code means you can understand what has been written. It requires intention-revealing names and is best achieved by using Programming by Intention (see Chapter 1, Programming by Intention). Unreadable code, of course, is code you can't understand when you read it. Poor names, tight coupling, and big methods/classes contribute greatly to the unreadability of code.
  • Encapsulation. Encapsulation is more than mere data hiding. The type of an object is one of the most important things to hide. Design patterns are really about hiding: object type, cardinality, which function is being used, order, optional behavior, construction, and more. The pathology of encapsulation is when you must know how the code you are using is implanted in order to use it properly. This often means you know the implementation type of the object being used or know something about cardinality, order, and so on.
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