Class C from assembly A1 implements interface from assembly A2. When using C, need to reference both A1 and A2

This is by design, according to the answers in this SO question

But I really don't want to reference both assemblies, it feels like I'm breaking encapsulation (the users of A1 shouldn't know that A1 uses A2 for its implementation...)

I thought of moving the interface definition to another assembly, let's call it "Core", and have both A2 and A1's client reference it. This feels cleaner to me.

My question is: Is this good design? Or is there a standard .NET solution to this that I'm not awar开发者_运维知识库e of? On the other hand, I worry that "Core" will end up being a nasty mix of totally unrelated interfaces... What do you think?

---

First of all, this doesn't break encapsulation.

Encapsulation means that the implementation details are not relevant - so long as you program to the interface, encapsulation is intact.

Secondly - if you want to use both the interface and implementation, you need to reference the assemblies both are in (disregarding plug-in architectures). How else would your code work? If there is no reference to the implementation, you can't instantiate a concrete type. If there is no reference to the interface, you can't use it in your code.

---

C# does not have private inheritance. If class A1 implements interface A2, then that is public information, which is exposed to users of class A1, exactly as though A2 were a base class and not an interface.

Yes, you must reference both assemblies.

---

I solved it to my satisfaction, please tell me what you think:

(Warning: this is IDE-specific, don't know if I could pull it off in, say, SharpDevelop)

1. In A1, instead of referencing the A2 assembly, in Visual Studio, right-click the A1 project and select "Add Existing Item". Select the interface file. Before pressing the Add Button, notice it's a dropdown button: drop it and select "Add as Link". If you don't do it this way, you'll have to mantain multiple copies of the interface, which is a hassle

2. Remove the reference from A1 to A2 (if all you used from it was the interface)

3. Voila! A1's clients only need a reference to A1. I think this is because now the interface is a type which is defined in both the A1 and A2 assemblies. I don't think that endangers manteinance, because the interface is still defined in only one source code file. Ok, its's compiled into two assemblies, so it's a sort of "binary duplication", but I don't think that's bad... Do you?