Skip to main content

Lists or Objects

"Our rule of thumb is that we try to limit passing around types with generics (the types closed in angle brackets). Particularly when applied to collections, we view it as a form of duplication. It's a hint that there's a domain concept that should be extracted into a type." Growing Object-Oriented Software, Guided by Tests - Steve Freeman, Nat Pryce, page 136)

Example

Not ideal - business logic will leak.

Better - quotes are now encapsulated.

Why?

The benefit of the second approach is that you begin to force the collection to do the work. Consider a collection of quotes - using the first approach a developers' typical instinct would be to loop over the list and check each quote until the lowest quote was found. You could argue that this in turn violates the 'Tell Don't Ask' principle because very quickly you can find yourself digging down into objects. We would not do this with standalone objects, so collections should not be any different. Yet as developers we often avoid creating objects to encapsulate collections, despite this principle being taught in the early chapters of any OO programming beginners book.

Another key point of encapsulating collections is that you reduce duplication. If another part of the application needs to perform a check for the lowest quote, you'd end up either duplicating the code to loop over the quotes, or creating a helper method to do the actual processing. Using the collection means such features are only a method call away at all times.

In a recent code kata as well as a current set of work, we are applying some of the above concepts and finding a dramatic increase in the quality of our code. Those of you may have noticed that the above implementation inherits from a standard list, therefore it is indeed possible to still violate encapsulation and dig through the collection yourself. There are pros and cons to this approach, one benefit is all of the out of the box functionality you get for free - the ability to loop over the quotes (for displaying say) and return a count for example. The downside being developers can treat these collections as if they were a list.

In C# it is possible to use indexers or interfaces to improve the above implementation, though we tend to agree that it's up to the developers to do the "right" thing - in other words, not dive down into the collection. Interesting this very topic has been discussed on the excellent StackOverflow - I and others will sure agree that the answer(s) provided are well off the mark. Encapsulate your public collections - do not treat them as primitives!

Comments

Popular posts from this blog

Three Steps to Code Quality via TDD

Common complaints and problems that I've both encountered and hear other developers raise when it comes to the practice of Test Driven Development are: Impossible to refactor without all the tests breakingMinor changes require hours of changes to test codeTest setup is huge, slow to write and difficult to understandThe use of test doubles (mocks, stubs and fakes is confusing)Over the next three posts I will demonstrate three easy steps that can resolve the problems above. In turn this will allow developers to gain one of the benefits that TDD promises - the ability to refactor your code mercifully in order to improve code quality.StepsStop Making Everything PublicLimit the Amount of Dependencies you Use A Unit is Not Always a Method or ClassCode quality is a tricky subject and highly subjective, however if you follow the three guidelines above you should have the ability to radically change implementation details and therefore improve code quality when needed.

DRY vs DAMP in Tests

In the previous post I mentioned that duplication in tests is not always bad. Sometimes duplication becomes a problem. Tests can become large or virtually identically excluding a few lines. Changes to these tests can take a while and increase the maintenance overhead. At this point, DRY violations need to be resolved.SolutionsTest HelpersA common solution is to extract common functionality into setup methods or other helper utilities. While this will remove and reduce duplication this can make tests a bit harder to read as the test is now split amongst unrelated components. There is a limit to how useful such extractions can help as each test may need to do something slightly differently.DAMP - Descriptive and Meaningful PhrasesDescriptive and Meaningful Phrases is the alter ego of DRY. DAMP tests often use the builder pattern to construct the System Under Test. This allows calls to be chained in a fluent API style, similar to the Page Object Pattern. Internally the implementation wil…

Coding In the Real World

As a student when confronted with a problem, I would end up coding it and thinking - how do the professionals do this?For some reason I had the impression that once I entered the industry I would find enlightenment. Discovering the one true way to write high quality, professional code.It turns out that code in industry is not too far removed from the code I was writing back when I knew very little.Code in the real world can be:messy or cleanhard or easy to understandsimple or complexeasy or hard to changeor any combination of the aboveVery rarely will you be confronted with a problem that is difficult. Most challenges typically are formed around individuals and processes, rather than day to day coding. Years later I finally have the answer. Code in the real world is not that much different to code we were all writing when we first started out.If I could offer myself some advice back in those early days it would be to follow KISS, YAGNI and DRY religiously. The rest will fall into plac…

Feature Toggles

I'm a fan of regular releasing. My background and experience leads me to release as regularly as possible. There are numerous benefits to regular releases; limited risk, slicker release processes and the ability to change as requirements evolve.The problem with this concept is how can you release when features are not functionally complete?SolutionIf there is still work in progress, one solution to allow frequent releases is to use feature toggles. Feature toggles are simple conditional statements that are either enabled or disabled based on some condition.This simple example shows a feature toggle for an "Edit User" feature. If the boolean condition is false, then we only show the "New User" feature and the "Admin" feature. This boolean value will be provided by various means, usually a configuration file. This means at certain points we can change this value in order to demonstrate the "Edit User" functionality. Our demo environment could …

Reused Abstraction Principle

This is the second part of my series on abstractions.Part 1 - AbstractionsPart 3 - Dependency Elimination PrincipleThe Reused Abstraction Principle is a simple in concept in practice, but oddly rarely followed in typical enterprise development. I myself have been incredibly guilty of this in the past.Most code bases have a 1:1 mapping of interfaces to implementations. Usually this is the sign of TDD or automated testing being applied badly. The majority of these interfaces are wrong. 1:1 mappings between interfaces and implementations is a code smell.Such situations are usually the result of extracting an interface from an implementation, rather than having the client drive behaviour.These interfaces are also often bad abstractions, known as "leaky abstractions". As I've discussed previously, these abstractions tend to offer nothing more than simple indirection.ExampleApply the "rule of three". If there is only ever one implementation, then you don't need …