Skip to main content

Getters and Setters are Evil

Update: There is a new version of this post.


I've been programming with OO languages since I was seventeen yet in the last week I've had what is without doubt one of the biggest learning experiences since I've started.

Numerous developers that I've worked with claimed that we aren't doing OO properly. By we I mean software developers as a whole. Their argument being having all your code defined in classes does not mean you are obeying OO principles. By this they are often referring to the "Tell Don't Ask" principle. One particular individual at Codeweavers introduced me to idea that getters and setters are evil. While not true at face value, this statement is to get you thinking about what you expose to the outside world. Consider one of the founding pillars of OO programming; encapsulation.

Encapsulation states that an objects internal state should be just that, internal. If we want a object to do something we should tell it. We shouldn't care how its done either. The more I begin to think about what I'm programming the more I begin to question myself. In a recent programming session this was even more apparent. I stumbled across a situation in which I wished to hide a objects internal state, and in turn tell the object to do stuff. The problem I encountered was how the hell do I display the state of this object to the user (say on a GUI) without adding a load of properties (getters/setters).

Had I added the properties to the object I could ignore the methods on the object and just dig down and fiddle the objects internal state from the outside. This was not right, alarms bells were going off yet I was unsure how to solve this. Thankfully some inspiration from a helpful StackOverflow user and advice from a collegue pointed me in the right direction.

The solution was simple and can be summarised in the following pseudo code:

A more encapsulated approach could be:

A business object should property free, or at least only able to be updated from the outside world by asking it to do something. Its internal state may be internal to the class itself, or there may be a DTO passed in at construction it matters not. The Writer in this case is an abstraction around some form of output. We could have a console writer, HTML writer, Json writer and so on. By inverting the dependency we can avoid adding properties to the business object. Any consumer of this object must invoke the business object's methods - aka tell the object to do stuff. There is no way of the outside world modifying this objects internal state without abiding by the business rules. What's nice about this revelation?

There are many examples of this pattern at Codeweavers, yet I was unaware of the problem it was solving. By being burned by this issue personally the reason for patterns such as the one detailed above become much clearer and stand out. Whats better is when this problem crops up again I'll be able to handle it.

Properties or accessors have their place. They are required for DTOs, frameworks and certain language features, yet as with any tool their usage should always be considered. Blindly adding properties to a object, or worse, having the IDE auto generate accessors to an objects state is a clear problem. The biggest lesson I've took away is that even for input/output the use of accessors is not required. As usual the Codeweavers saying of "if it feels wrong, it probably is" still holds true and on that I'm off to try and write some proper OO code for the first time in six years...

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 …