如何为通用接口创建具有其他类型的通用扩展方法

Question

Today I encountered a small problem, and unfortunately I have not found a good solution. I would like to create a extension method for some generic interface. This method accepts a different type of a generic parameter, as seen below

public interface IGenericInterface<TSource>
{
    void DoSomething<TDest>();
}

DotNetFiddle

How to call a DoSomething2 method exactly in the same way as DoSomething method (without passing first type)?

public void DoSomething<TDest>()
//Called like below
testClass.DoSomething<object>();

instead of (like my current signature)

public static void DoSomething2<TDest, TSource>(this IGenericInterface<TSource> interf)
//called like below
testClass.DoSomething2<string, object>(); // have to repass object type

I know that the compiler can not automatically infer the second type ( link ). But I'm curious if anyone has found a solution.

Answer 1

Your problem is the argument - you're depending on type inference to handle the first generic type, but then you want to explicitly specify the second one - that just isn't possible in C#.

Instead, why not change the type of the argument?

public static void DoSomething3<T, T2>(this IGenericInterface<T> interf, T2 parameter)
//called like below
testClass.DoSomething3((object)3);

With this, T is inferred based on testClass (as long as it's not ambiguous), and T2 is inferred based on (object)3 .