多个类型参数-约束到相同的基类？

Question

Let's say we have this class structure:

interface A { }
interface A1 : A { }
interface A2 : A { }
class B : A1 { }
class C : A1 { }
class D : A2 { }
class E : A2 { }

And I want to declare a method with this header:

public void DoSomething<T, U>()
    where T : A
    where U : A
    <and also where U inherits/implements same parent as T>

It needs to allow DoSomething<B, C>() :

• where T : A is satisfied - B implements A
• where U : A is satisfied - C implements A
• <and also where U inherits/implements same parent as T> is satisfied because both B and C implement A1
• DoSomething<D, E>() is also allowed because D and E both implement A2

But it needs to not allow DoSomething<B, D>() :

• where T : A is satisfied - B implements A
• where U : A is satisfied - C implements A
• <and also where U inherits/implements same thing as T> is not satisfied because B implements A1 but D does not.

Is this possible?

(I think I've butchered the use of the word 'parent' there, but hopefully it's still clear)

Answer 1

The only thing you can do is to provide a third generic type parameter that will let you specify which interface both T and U have to implement:

public void DoSomething<T, U, V>()
    where T : V
    where U : V
    where V : A

Now you can do DoSomething<D, E, A1>() but not DoSomething<B, D, A1>() .