Extract Method is one of the most basic and common refactorings. In Refactoring: Improving the Design of Existing Code, Martin Fowler gives the following motivation for using Extract Method:
“Extract Method is one of the most common refactorings I do. I look at a method that is too long or look at code that needs a comment to understand its purpose. I then turn that fragment of code into its own method.
I prefer short, well-named methods for several reasons. First, it increases the chances that other methods can use a method when the method is finely grained. Second, it allows the higher-level methods to read more like a series of comments. Overriding also is easier when the methods are finely grained.
It does take a little getting used to if you are used to seeing larger methods. And small methods really work only when you have good names, so you need to pay attention to naming. People sometimes ask me what length I look for in a method. To me length is not the issue. The key is the semantic distance between the method name and the method body. If extracting improves clarity, do it, even
if the name is longer than the code you have extracted.”
Few would argue with the benefits of this refactoring.
‘For years authors and consultants (like me) have been telling us that functions should do one thing. They should do it well. They should do it only.
The question is: What the hell does “one thing” mean?
After all, one man’s “one thing” might be someone else’s “two things”.’
Uncle Bob’s post provides an example of extracting until nothing else can be done, and then he ends with this comment:
“Perhaps you think this is taking things too far. I used to think so too. But after programming for over 40+ years, I’m beginning to come to the conclusion that this level of extraction is not taking things too far at all. In fact, to me, it looks just about right.
So, my advice: Extract till you just can’t extract any more. Extract till you drop.”
As he predicts, many people do think he’s going too far. Here’s a couple excerpts from the post’s comments:
“Following the flow of the data through the fully extracted version becomes difficult, since the developer will need to jump around constantly throughout the body of the class.
If the goal is to make development and maintenance easier and fully extracting the class makes it more difficult for a developer to follow the flow of the data is it better to fully extract just for the sake of following a rule?
My point is that patterns in code are easier to see when things are not broken down into such small chunks. At the fully decomposed state it isn’t obvious that an Adapter on the Matcher would simply fit into place. By decomposing the methods so fine you lose context, so much so it isn’t evident how the method relates to the accomplishing the goal of the class.”
‘A function by definition, returns 1 result from 1 input. If there’s no reuse, there is no “should”. Decomposition is for reuse, not just to decompose. Depending on the language/compiler there may be additional decision weights.
What I see from the example is you’ve gone and polluted your namespace with increasingly complex,longer,more obscure, function name mangling which could have been achieved (quick and readable) with whitespace and comments. To mirror a previous poster, I rather see a javadoc with proper commenting than to trace what’s going on for such a simplistic case. I’m afraid to ask what you plan to do when the class is more complex and symbolExpression(..) isn’t descriptive enough!’
These arguments make a good point. However, these arguments also apply to object-oriented code in general. Reading and navigating object-oriented code can often be more difficult than its procedural counterparts. However, we hope to overcome these disadvantages by creating a structure that is more readable and reusable overall.
In Uncle Bob’s example, the newer, more granular methods provide a more complete and accurate view of the behaviors and capabilities of the SymbolReplacer class. In isolation, it might appear as overkill and “polluted namespaces”. However, if you were maintaining a large codebase and needed to understand how to use (or reuse) SymbolReplacer, I believe Uncle Bob’s approach would make your task much easier. You don’t need to read through javadoc (as one commenter prefers). Instead, the method names are more clear, the size is smaller and easier to override, and the class itself almost becomes readable English. In my opinion, these advantages outweigh the loss of navigability.
But, perhaps, as Martin Fowler mentions “it does take a little getting used to”. Uncle Bob said almost the same thing: “Perhaps you think this is taking things too far. I used to think so too. But after programming for over 40+ years, I’m beginning to come to the conclusion that this level of extraction is not taking things too far at all. In fact, to me, it looks just about right.”
With the wisdom of those two, I think we owe it to ourselves to set aside our skepticism and give it a real try. We can come back later, compare results, and make a decision then. I have found that those who are willing to try their advice, in the end, never go back. Perhaps, you will will find that your code gets cleaner and opportunities for reuse start showing themselves in surprising ways.