C# Interfaces with optional methods

c# interface versioning
Nelson Rothermel picture Nelson Rothermel · Mar 4, 2010 · Viewed 42.2k times · Source

I understand that interfaces are contracts and any changes (even additions) break any dependent code. However, I could have sworn I read something a while back that one of the recent .NET versions (3, 3.5??) added a new attribute that could be applied to new interface members. This attribute allowed versioning and/or making members optional. It would have been something like:

interface ITest
{
    void MethodOne();

    [InterfaceVersion(2)]
    void MethodTwo();
}

I have looked high and low for this but just can't seem to find it. I am wondering whether I simply misunderstood whatever I think I read and there is no such thing. Does someone have any insight?

Answer

Lasse V. Karlsen picture Lasse V. Karlsen · Mar 4, 2010

You should create two interfaces:

interface ITest
{
    void MethodOne();
}

interface ITest2 : ITest
{
    void MethodTwo();
}

This would also make it clear which functionality requires which version of your interfaces, so that you don't have to check whether the class implementing the interface is implementing just one, or both, methods.

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