CRTP in C#
C++ developers are well familiar with the CRTP - Curiously Recurring Template Pattern, where a class can derive from another class, specifying itself as a template parameter.
Every now and then I wish this pattern can be used in C#. If you attempt to implement it C++ style, you would get a compile error:
This is probably a point at which you give up and find another way of doing things. It is, however, possible to implement a fully functioning curiously recurring class system in C# by simply adding a constraint to the base class like so:
If you attempt to read the constraint your brain will probably spin in infinite circles trying to figure out how it is even possible for a type parameter to be the same as the class itself. The fact that it works, however, is not more magic than the C++ version, where the recursive nature of the class declaration simply compiles. What the constraint really says is that *T is a class that derives from Base
Another observation. You cannot use
Base<T> by itself. It must be inherited from. The
abstract keyword is not compulsory, it will compile without it. You just won’t be able to declare an instance of
Base<T> by itself.
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