In a small piece of code

This post appeared originally on Codesai’s Blog.

In a previous post we talked about positional parameters and how they can suffer from Connascence of Position, (CoP). Then we saw how, in some cases, we might introduce named parameters to remove the CoP and transform it into Connascence of Name, (CoN), but always being careful to not hiding cases of Connascence of Meaning, (CoM). In this post we’ll focus on languages that don’t provide named parameters and see different techniquess to remove the CoP.

Let’s see an example of a method suffering of CoP:

In languages without named parameters (the example is written in Java), we can apply a classic^[1] refactoring technique, Introduce Parameter Object, that can transform CoP into CoN. In this example, we introduced the ClusteringParameters object:

which eliminates the CoP transforming it into CoN:

In this particular case, all the parameters passed to the function were semantically related, since they all were parameters of the clustering algorithm, but in many other cases all the parameters aren’t related. So, as we saw in our previous post for named parameters, we have to be careful of not accidentally sweeping hidden CoM in the form of data clumps under the rug when we use the Introduce Parameter Object refactoring.

In any case, what it’s clear is that introducing a parameter object produces much less expressive code than introducing named parameters. So how to gain semantics while removing CoP in languages without named parameters?

One answer is using fluent interfaces^[2] which is a technique that is much more common than you think. Let’s have a look at the following small piece of code:

This is just a simple test. However, just in this small piece of code, we can find two examples of removing CoP using fluent interfaces and another example that, while not removing CoP, completely removes its impact on expressiveness. Let’s look at them with more detail.

The first example is an application of the builder pattern using a fluent interface^[3].

Applying the builder pattern provides a very specific^[4] internal DSL that we can use to create a complex object avoiding CoP and also getting an expressiveness comparable or even superior to the one we’d get using named parameters.

In this case we composed two builders, one for the SafetyRange class:

and another for the Alarm class:

Composing builders you can manage to create very complex objects in a maintanable and very expressive way.

Let’s see now the second interesting example in our small piece of code:

This assertion using hamcrest is so simple that the JUnit alternative is much clearer:

but for more than one parameter the JUnit interface starts having problems:

Which one is the expected value and which one is the actual one? We never manage to remember…

Using hamcrest removes that expressiveness problem:

Thanks to the semantics introduced by hamcrest^[6], it’s very clear that the first parameter is the actual value and the second parameter is the expected one. The internal DSL defined by hamcrest produces declarative code with high expressiveness. To be clear hamcrest is not removing the CoP, but since there are only two parameters, the degree of CoP is very low^[7]. The real problem of the code using the JUnit assertion was its low expressiveness and using hamcrest fixes that.

For us it’s curious to see how, in trying to achieve expressiveness, some assertion libraries that use fluent interfaces have (probably not being aware of it) eliminate CoP as well. See this other example using Jasmine:

Finally, let’s have a look at the last example in our initial small piece of code which is also using a fluent interface:

This is Mockito’s way of defining a stub for a method call. It’s another example of fluent interface which produces highly expressive code and avoids CoP.

Summary.

We started seeing how, in languages that don’t allow named parameters, we can remove CoP by applying the Introduce Parameter Object refactoring and how the resulting code was much less expressive than the one using the Introducing Named Parameters refactoring. Then we saw how we can leverage fluent interfaces to remove CoP while writing highly expressive code, mentioned internal DSLs and showed you how this technique is more common that one can think at first by examining a small piece of code.

References.

Books.

• Refactoring: Improving the Design of Existing Code, Martin Fowler
• Growing Object-Oriented Software Guided by Tests, Nat Pryce and Steve Freeman.
• Refactoring Ruby, Jay Fields, Kent Beck, Martin Fowler, Shane Harvie

Posts.

• Refactoring Ruby: Bad Smells in Code, Jay Fields, Kent Beck, Martin Fowler, Shane Harvie
• Builders vs option maps, Kyle Kingsbury
• Refactoring tests using builder functions in Clojure/ClojureScript, Manuel Rivero
• Remove data structures noise from your tests with builders, Carlos Blé
• Two examples of Connascence of Position, Manuel Rivero, Fran reyes
• About Connascence, Manuel Rivero

Footnotes:

[1] See Martin Fowler's Refactoring, Improving the Design of Existing Code book.

[2] Of course, fluent interfaces are also great in languages that provide named parameters.

[3] Curiosly there're alternative ways to implement the builder pattern that use options maps or named parameters. Some time ago we wrote about an example of using the second way: Refactoring tests using builder functions in Clojure/ClojureScript.

[4] The only purpose of that DSL is creating one specific type of object.

[5] For us the best explanation of the builder pattern and how to use it to create maintanable tests is in chapter 22, Constructing Complex Test Data, of the wonderful Growing Object-Oriented Software Guided by Tests book.

[6] hamcrest is a framework for writing matcher objects allowing 'match' rules to be defined declaratively. We love it!

[7] See our previous post about CoP.

Interesting Talk: "re-frame your ClojureScript applications"

I've just watched this interesting talk by Shaun Mahood

• re-frame your ClojureScript applications

Interesting Talk: "Testing Stateful and Concurrent Systems Using test.check"

I've just watched this wonderful talk by Eric Normand

• Testing Stateful and Concurrent Systems Using test.check

Notes on SRP from Agile Principles, Practices and Patterns book

I think that if you rely only on talks, community events, tweets and posts to learn about a concept, you can sometimes end up with diluted (or even completely wrong) versions of the concept due to broken telephone game effects. For this reason, I think it's important to try instead to get closer to the sources of the concepts you want to learn.

Lately I've been doing some study on object-oriented concepts doing an effort to get closer to the sources. These are the resulting notes on Single Responsibility Principle I've taken from the chapter devoted to it in Robert C. Martin's wonderful Agile Principles, Practices and Patterns in C# book:

• "This principle was described in the work of [Larry Constantine, Ed Yourdon,] Tom DeMarco and Meilir Page-Jones. They called it cohesion, which they defined as the functional relatedness of the elements of a module" <- [!!!]
• "... we modify that meaning a bit and relate cohesion to the forces that cause a module, or a class, to change"
• [SRP definition] -> "A class should have only one reason to change"
• "Why was important to separate [...] responsibilities [...]? The reason is that each responsibility is an axis of change" <- [related with Mateu Adsuara's complexity dimensions]
• "If a class has more than one responsibility the responsibilities become coupled" <- [related with Long Method, Large Class, etc.] <- [It also eliminates the possibility of using composition at every level (functions, classes, modules, etc.)] "Changes to one responsibility may impair or inhibit the class ability to meet the others. This kind of coupling leads to fragile designs" <- [For R. C. Martin, fragility is a design smell, a design is fragile when it's easy to break]
• [Defining what responsibility means]
  • "In the context of the SRP, we define a responsibility to be a reason for change"
  • "If you can think of more than one motive for changing a class, that class has more than one responsibility. This is sometimes difficult to see"
• "Should [...] responsibilities be separated? That depends on how the application is changing. If the application is not changing in ways that cause the [...] responsibilities to change at different times, there is no need to separate them." <- [applying Beck's Rate of Change principle from Implementation Patterns] "Indeed separating them would smell of needless complexity" <- [Needless Complexity is a design smell for R. C. Martin. It's equivalent to Speculative Generality from Refactoring book]
• "An axis of change is an axis of change only if the changes occur" <- [relate with Speculative Generality and Yagni] "It's not wise to apply SRP, or any other principle if there's no symptom" <- [I think this applies at class and module level, but it's still worth it to always try to apply SRP at method level, as a responsibility identification and learning process]
• "There are often reasons, having to do with the details of hardware and the OS [example with a Modem implementing two interfaces DateChannel and Connection], that force us to couple things that we'd rather not couple. However by separating their interfaces, we [...] decouple[..] the concepts as far as the rest of the application is concerned" <- [Great example of using ISP and DIP to hide complexity to the clients] "We may view [Modem] as a kludge, however, note that all dependencies flow away from it." <- [thanks to DIP] "Nobody needs to depend on this class [Modem]. Nobody except main needs to know it exists" <- [main is the entry point where the application is configured using dependency injection] "Thus we've put the ugly bit behind a fence. It's ugliness need not leak out and pollute the rest of the app"
• "SRP is one of the simplest of the principles but one of the most difficult to get right"
• "Conjoining responsibilities is something that we do naturally"
• "Finding and separating those responsibilities is much of what software design is really about. Indeed the rest of the principles we discuss come back to this issue in one way or another"

Agile Principles, Practices and Patterns in C# is a great book that I recommend to read. For me getting closer to the sources of SOLID principles has been a great experience that has helped me to remove illusions of knowledge I had developed due to the telephone game effect of having learned it through blogs and talks.

Other posts in this series:

• Notes on OCP from Agile Principles, Practices and Patterns book

Interesting Talk: "Repl Driven Development"

I've just watched this wonderful talk by Stuart Halloway

• Repl Driven Development