Is there a reasonable approach to "default" type parameters in C# Generics?

c# generics types default parameters
el2iot2 picture el2iot2 · Apr 2, 2009 · Viewed 30.8k times · Source

In C++ templates, one can specify that a certain type parameter is a default. I.e. unless explicitly specified, it will use type T.

Can this be done or approximated in C#?

I'm looking for something like:

public class MyTemplate<T1, T2=string> {}

So that an instance of the type that doesn't explicitly specify T2:

MyTemplate<int> t = new MyTemplate<int>();

Would be essentially:

MyTemplate<int, string> t = new MyTemplate<int, string>();

Ultimately I am looking at a case wherein there is a template that is fairly widely used, but I am considering expanding with an additional type parameter. I could subclass, I guess, but I was curious if there were other options in this vein.

Answer

Reed Copsey picture Reed Copsey · Apr 2, 2009

Subclassing is the best option.

I would subclass your main generic class:

class BaseGeneric<T,U>

with a specific class

class MyGeneric<T> : BaseGeneric<T, string>

This makes it easy to keep your logic in one place (the base class), but also easy to provide both usage options. Depending on the class, there is probably very little extra work needed to make this happen.

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