Collections as decorators in C#

Question

Hey there!

We've been hit with a pretty "obvious" problem while designing a collections infrastructure: suppose you need to implement many (sub)types of collections. One of the aspects is storage-related: list, array etc, while the other is behavior-related: ordered, remove only, observable (the one that fires an event upon every change) etc.

Obviously (again), the requirement maps directly to the well-known Decorator design pattern (list, array), where the storage-related aspect will be decorated by multiple behavioral (ordered, observable etc).

It would be great to know about something similar that had been already implemented by someone. Hence, if possible - please recommend/refer to any well-maintained third-party library that would meet the requirements, mentioned above.

Thanks so far :)

Answer 1

I think you misunderstood something:

Decorators are used to modify and add behaviour primarily at runtime. But the properties of collections that you cited need to be available at compile time. A decorator is completely unsuited to add more methods to an existing class.

While it is possible to decompose these traits of collections into interfaces (and indeed has been done ¹⁾), this isn’t really what a decorator is about: a decorator wraps an existing class implementing the same interface. For collections, inheritance will make more sense (or may indeed be required) instead of composition.

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¹⁾ A few years, I started developing my own such library, Containers.NET but since preliminary benchmarks showed just how much faster the native .NET containers were, even though Containers.NET did not have any added overhead, I stopped the project before it got very far.