Q:

How to call generic method with stronger constraint?

namespace Test
{
    #region Not my code
    public interface IAdditional
    {
    }
    public interface ISome
    {
        ISomeOther<T> GetSomeother<T>() where T : class;
    }
    public interface ISomeOther<T> where T : class
    {
        void DoFoo(T obj);
    }
    public class AnotherClass<T> where T : class
    {
    }
    public static class StaticClass
    {
        public static void DoBar<T>(AnotherClass<T> anotherClass, T obj) where T : class, IAdditional
        {
        }
    }
    #endregion

    #region MyCode
    public class SomeOtherImp<T> : ISomeOther<T> where T : class, IAdditional //Have to add IAdditional constraint to call StaticClass.DoBar
    {
        private AnotherClass<T> _anotherClass;
        public void DoFoo(T obj)
        {
            StaticClass.DoBar<T>(_anotherClass, obj); //I do need to call StaticClass.DoBar here....
        }
    }
    public class ISomeImp : ISome
    {
        public ISomeOther<T> GetSomeother<T>() where T : class
        {
            return new SomeOtherImp<T>(); //Can't do this no IAdditional constraint on T
        }
    }
    #endregion
}

I was forced to add IAdditional to SomeOtherImp to be able to call StaticClass.DoBar.
And now I can't implement ISome with SomeOtherImp<T>.

A:

Do you mean that you want to be able to call the Get method? If you can edit the interface ISome, try this:
public interface ISome
{
    T Get<T>() where T:class, ISomeInterface
}

...otherwise you're going to have to use reflection:
public class Foo : ISome
{
    public T Get<T>() where T:class
    {
        if (!typeof(ISomeInterface).IsAssignableFrom(typeof(T))) throw new Exception();
        return (T)typeof(SomeStaticClass).GetMethod("Create").MakeGenericMethod(new [] {typeof(T)}).Invoke();
    }
}

