Autofac - injecting based on generic interface and concrete type

Question

I have the following interface

public interface ICheckEvaluator<in TCheck> where TCheck : ResourceCheck

that needs to be injected with the following implementation:

public class OutageCheckEvaluator : ICheckEvaluator<OutageCheck>

Can someone provide an advice as to how this can be done? OutageCheck inherits from ResourceCheck:

public partial class OutageCheck : ResourceCheck

The following method didnt work:

builder.RegisterType<OutageCheckEvaluator>().As<ICheckEvaluator<OutageCheck>>();

as Autofac receives ICheckEvaluator(ResourceCheck) to implement and cannot match it to ICheckEvalutor(OutageCheck)

Appreciate any advice here.

Answer 1

You could resolve those Evaluators by using e.g. reflection.

public class AutofacTest
{
    [Test]
    public void Test()
    {
        var builder = new ContainerBuilder();
        builder.RegisterType<OutageCheckEvaluator>().As<ICheckEvaluator<OutageCheck>>();
        var container = builder.Build();

        var listOfChecks = new List<ResourceCheck> { new OutageCheck() };
        foreach (var check in listOfChecks)
        {
            var interfaceType = typeof(ICheckEvaluator<>).MakeGenericType(check.GetType());
            var evaluator = container.Resolve(interfaceType);
            Debug.WriteLine(evaluator);
        }
    }
}

public interface ICheckEvaluator<in TCheck> where TCheck : ResourceCheck { }

public class OutageCheckEvaluator : ICheckEvaluator<OutageCheck> { }

public class OutageCheck : ResourceCheck { }

public class ResourceCheck{}

but the problem is that since generic parameter is contravariant you cannot do any of those casts

var test = new OutageCheck() as ICheckEvaluator<ResourceCheck>;
var evaluator = container.Resolve(interfaceType) as ICheckEvaluator<ResourceCheck>;

Is there any special need you have ICheckEvaluator<in TCheck> instead of ICheckEvaluator<out TCheck>?