The random utterances of David Arno

Do you have a compatible Apple device, but are unsure whether to install Apple’s latest OS on it? If so, I’ve created a handy flowchart to help you decide.

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Design patterns: who really uses them? Are they just ways of overcoming limitations in Java? Are they an idea that has had its time? Do they really aid understanding of ideas between programmers, or do they just cause more confusion? Or, are they a great, but often misunderstood, idea that is still relevant today and that can be applied to all languages? After much thought and discussion with unsuspecting folk who have suffered a string of daft questions from me, I finally feel able write down my take on software design patterns and my conclusions might surprise many that know me.

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Recently I created a very simple framework, SuccincT. At it’s core is the ISuccess<T> interface. As I explained in a previous post though, by itself that interface isn’t much use. C# lacks the ability to define constraints on an implementation of ISuccess<T>, save through comments. The idea behind it was that an implementation should throw an exception if its Value is read when Success is false, but there is no way to guarantee that an implementation will exhibit this behaviour. This bugs me.

Unrelated to SuccincT, I’m a fan of defining data objects via interfaces, rather than concrete types. By “data object”, I mean any object that encapsulates a set of values. These might be used to avoid multiple parameters to a method or constructor, or to return a complex data set from a method. Data objects need not be immutable or serializable; they just need to be simple to use without causing problems when it comes to testing. As I like to encapsulate data, I like the setters of data objects to be internal, which does cause problems with testing. Thus why I like to use interfaces: the test class can define its own implementation, rather than having to fight against encapsulation. However, for every interface I create, I have to create at least one class too. This adds needless code to projects, which also bugs me.

These two things – wanting interfaces to define a more detailed contract and wanting to avoid having to write data object classes that can be 100% inferred from the interface – set me thinking: could I create some way of extending interfaces and avoiding writing data object classes?

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Equality in C# is an odd beast. At first glance, it seems very simple. Value types are compared by by value, objects are compared by reference and the comparison method can be overridden by a class if it wants to. For example, the String class compares the string contents, rather than comparing by reference. There are also sensible “best practice” rules suggested by Microsoft, such as avoiding comparing mutable objects by value, only by reference. All is not as it seems though as the following series of NUnit tests show. All the tests pass and thus demonstrate some aspect of equality in C#.

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The two ways of checking for equality in C# – using == and .Equals() – can be modified for individual types. It is important to remember though that override and overload are two very different things in C#: .Equals() can be both overridden and overloaded, whereas == can only be overloaded. This set of tests demonstrate the significant effects this subtle difference can have on equality comparisons.

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With .NET 2.0, Microsoft introduced the IEquatable interface. It introduced a typesafe Equals() method that could be used to speed up comparisons in the new generic collections. It speeded up those comparisons by avoiding the need for casting and boxing, which the Object.Equals() suffered from. The IEquatable interface is a dangerous beast though as it can lure the unwary into thinking it rationalised equality in C#. This set of tests sets out to demonstrate how quite the opposite occurred: it simply made things worse.

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The .NET framework is getting on a bit. Many users of the .NET framework are either resistant to API changes, or are stuck with binary-only 3rd party tools that would break with API changes. As a consequence of these two things, the .NET framework has aspects to it that go against modern thinking, but we are stuck with them. The solution to this is often to encapsulate those features within newer frameworks, which offer “best practice” facades on to those features. SuccincT is one such framework.

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This blog post was inspired by a brief twitter conversation between myself and Mark Seeman on how, in the future, developers will likely just write tests and how the computer will generate the code to make those tests pass.

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QCon is a large conference, with around six parallel tracks, offering talks on a range of subjects. Normally when visiting QCon, I skip between these tracks as the day progresses. That was certainly my plan for day 2 this year, but as the day progressed, I realised one track offered me a great opportunity to take away a good cross-section of ideas; ideas that some might no doubt find controversial: agile can be too process-bound and people are more important than processes.

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