通用类型，该通用类型实现具有多个类型的通用接口

Question

I have this interface:

interface a<A, B>
{
    A retA();
    B retB();
}

and I would like to create a generic method that takes a type which implements this interface.

private void fa<T>() where T : a<A, B>, new(){ code}

This line doesn't work ( compile time error ):

the type or namespace A could not be found, the type or namespace B could not be found

Thank you for your help

Answer 1

You have three generic parameters ( A , B , T ) within fa method; each of them should be either declared or resolved ; there are several ways to do it, eg

  public class Sample1<A, B> {
    // Class declares A and B; method declares T
    private void fa<T>() where T : a<A, B>, new() {
      // Code
    }
  }

  public class Sample2 {
    // Method declares all three generic types: A, B and T
    private void fa<T, A, B>() where T : a<A, B>, new() {
      // Code 
    }
  }

  public class Sample3 {
    // Method declares T; A and B are resolved (explict types: string and int)
    private void fa<T>() where T : a<string, int>, new() {
      // Code
    }
  }

  public class Sample4<A> {
    // Class declares A; method declares T; B is resolved (explicit type int)
    private void fa<T>() where T : a<A, int>, new() {
      // Code
    }
  }

Etc.

Answer 2

德米特里·拜琴科（Dmitry Bychenko）给出的答案：

fa<T, A, B>() where T : a<A, B>, new(){ code}