Nested contravariant generics

[CoskunSunali]

Is it possible to satisfy the following requirement using DryIoc? I am trying to implement a simple event handler where A is base of B and anything related to B should trigger A as well. This is like what https://github.com/dadhi/DryIoc/blob/master/docs/DryIoc.Docs/OpenGenerics.md#generic-variance-when-resolving-many-services has as an example but the example there is covariant with the out keyword. However, event handlers usually are not expected to be covariant, they are rather contravariant because the event is passed in, not out.

E.g.: void HandleEvent(T eventData)

public static class DryIocContainer_GenericVarianceTest
{
    public static void Run()
    {
        var c = new Container();

        c.Register<IGenericType<A>, GenericType<A>>();
        c.Register<IGenericType<B>, GenericType<B>>();

        c.Register<IGenericTypeWrapper<IGenericType<A>>, GenericTypeWrapper<IGenericType<A>>>();
        c.Register<IGenericTypeWrapper<IGenericType<B>>, GenericTypeWrapper<IGenericType<B>>>();

        var genericTypes_A = c.ResolveMany<IGenericType<A>>(); // Gets A and B (expected)
        var genericTypes_B = c.ResolveMany<IGenericType<B>>(); // Gets B (expected)

        var genericTypeWrappers_A = c.ResolveMany<IGenericTypeWrapper<IGenericType<A>>>(); // Gets A (unexpected)
        var genericTypeWrappers_B = c.ResolveMany<IGenericTypeWrapper<IGenericType<B>>>(); // Gets A and B (unexpected)
    }
}

public interface IGenericTypeWrapper<in T> where T : class
{
}

public interface IGenericType<in T> where T : class
{
    void Do(T value);
}

public class GenericTypeWrapper<T> : IGenericTypeWrapper<T> where T : class
{
}

public class GenericType<T> : IGenericType<T> where T : class
{
    public void Do(T value)
    {
    }
}

public class A : IGenericType<A>
{
    public virtual void Do(A value)
    {
        // Do A
    }
}

public class B : A
{
    public override void Do(A value)
    {
        // Do B
    }
}

[dadhi]

Interesting question, will look

[CoskunSunali]

Okay, the example was completely wrong in terms of "expected" and "unexpected" parts I defined.

I defined both interfaces as covariant but the inner generic had to be contravariant. The following code satisfies everything. DryIoc handles it correctly! Great job, @dadhi . I will mark your reply as an answer so that the question is marked as Answered.

    public static class DryIocContainer_GenericVarianceTest2
    {
        public static void Run()
        {
            var c = new Container();

            c.Register<IGenericTypeWrapper<IGenericType<A>>, GenericTypeWrapper<IGenericType<A>>>();
            c.Register<IGenericTypeWrapper<IGenericType<B>>, GenericTypeWrapper<IGenericType<B>>>();

            var genericTypeWrappers_A = c.ResolveMany<IGenericTypeWrapper<IGenericType<A>>>(); // Gets A (expected)
            var genericTypeWrappers_B = c.ResolveMany<IGenericTypeWrapper<IGenericType<B>>>(); // Gets A and B (expected)
        }
    }

    public interface IGenericTypeWrapper<in T> where T : class
    {
        void Do(T value);
    }

    public interface IGenericType<out T> where T : class
    {
    }

    public class GenericTypeWrapper<T> : IGenericTypeWrapper<T> where T : class
    {
        public void Do(T value)
        {
        }
    }

    public class GenericType<T> : IGenericType<T> where T : class
    {

    }

    public class A : IGenericType<A>
    {
    }

    public class B : A
    {
    }

[dadhi]

Great to hear.

There is also a non-default WithVariantGenericTypesInResolve() rule to enable variance for the single service resolution.

Btw, if you interested in the MediatR alike variant request/handlers you may look inzo DryIoc.Messages namespace https://github.com/dadhi/DryIoc/blob/master/docs/DryIoc.Docs/DryIoc.Messages.md

[CoskunSunali]

There is also a non-default WithVariantGenericTypesInResolve() rule to enable variance for the single service resolution.

Is there an example of it somewhere in the docs? I did my best to find one but no luck so far and it is hard to understand what it helps with :)

Btw, if you interested in the MediatR alike variant request/handlers you may look inzo DryIoc.Messages namespace https://github.com/dadhi/DryIoc/blob/master/docs/DryIoc.Docs/DryIoc.Messages.md

Thanks, I will take a look at it. Appreciated.

[dadhi]

Is there an example of it somewhere in the docs?

Here are the tests for the related issue https://github.com/dadhi/DryIoc/blob/master/test/DryIoc.IssuesTests/GHIssue352_Consider_resolving_the_variance_compatible_open_generic_the_same_as_for_collection_of_open_generics.cs

[CoskunSunali]

Thanks @dadhi .

[CoskunSunali]

Hey @dadhi I have another question regarding open generics so thought it might be a better idea to continue within the same discussion. Just let me know if it's better for you if I create a new discussion.

My question is whether it is funny to try to do something like the following with DryIoc :)

Services.AddSingleton(
                typeof(ISuperWrapper<,>).MakeGenericType(typeof(IWrappedType<>), typeof(IResult)),
                typeof(SuperWrapper<>));

I know it is super ridiculous because IWrappedType<> and SuperWrapper<> would not even know which type parameter to use because type parameter counts are not equal but you thought so many magical things while developing DryIoc, I thought you might have an idea or just say don't even try it :)

[dadhi]

Huh, ok. It may be too strict of the check. I will try to lift it and check the result Tomorrow.

[CoskunSunali]

Thank you! Looking forward for testing it.

[dadhi]

The issue to track #406

[dadhi]

@CoskunSunali I have released DryIoc v4.8.0 with the fix.

[CoskunSunali]

It works! I will test a few scenarios and let you know how it goes. Thanks for the prompt reaction!