public class StrangeConversion 

{

    public class SomeClass { }

    public interface ISomeInterface { }

    public class Implementation : SomeClass, ISomeInterface { }

    public void Foo<T>() where T : class 

    {

        T x = (T)Factory();

        //Compile-error: Cannot convert type 'T' to 'SomeClass'

        SomeClass a = (SomeClass)x;

        //This is perfectly fine:

        SomeClass b = (SomeClass)(object)x;

​

        if (x is SomeClass c) 

        {

            //This works as well and 'c' contains the reference.

        }

    }

    private object Factory() 

    {

        return new Implementation();

    }

}