public class Program

{

    public static void Main()

    {

        ISomeCovariantInterface<object> covariant = new SomeClass<string>(); // works

        ISomeInterface<object> invariant = new SomeClass<string>(); // fails

    }

}

​

interface ISomeInterface<T>

{

}

​

interface ISomeCovariantInterface<out T> 

{

}

​

class SomeClass<T> : ISomeInterface<T>, ISomeCovariantInterface<T>

{

}