Support multiple constructors with reflection-based component registration

Support multiple constructors where the constructor parameters are able to be obtained from the container and based on the supplied autofac parameters. The variable nature of the autofac parameters would decide which constructor to select.

For example, given a simple type with two public constructors:

public class TwoConstructors
{
   readonly object _value;

   public TwoConstructors(IA value) => _value = value;
   public TwoConstructors(IB value) => _value = value;   
   public override string ToString() => _value.ToString();   
}

with simple types for the constructor parameters:

public interface IA { }
public interface IB { }
public class A : IA { public override string ToString() => "A"; }
public class B : IB { public override string ToString() => "B"; }

with reflection-based registration:

var containerBuilder = new ContainerBuilder();
containerBuilder.RegisterType<A>().As<IA>();
containerBuilder.RegisterType<B>().As<IB>();

It would be great if this reflection-based registration:

containerBuilder.RegisterType<TwoConstructors>();

would behave like this delegate-based registration:

containerBuilder.Register((componentContext, parameters) =>
{
   var ia = parameters.OfType<TypedParameter>().Where(typedParameter => typedParameter.Type == typeof(IA)).Select(typedParameter => (IA)typedParameter.Value).FirstOrDefault();
   if (ia != null)
      return new TwoConstructors(ia);

   var ib = parameters.OfType<TypedParameter>().Where(typedParameter => typedParameter.Type == typeof(IB)).Select(typedParameter => (IB)typedParameter.Value).FirstOrDefault();
   if (ib != null)
      return new TwoConstructors(ib);

   throw new DependencyResolutionException("Missing IA or IB parameter");
});

Today we receive the following expected exception:

  Unhandled Exception: Autofac.Core.DependencyResolutionException: An error occurred during the activation of a particular registration. See the inner exception for details. Registration: Activator = TwoConstructors (ReflectionActivator), Services = [TwoConstructors], Lifetime = Autofac.Core.Lifetime.CurrentScopeLifetime, Sharing = None, Ownership = OwnedByLifetimeScope ---> Cannot choose between multiple constructors with equal length 1 on type 'TwoConstructors'. Select the constructor explicitly, with the UsingConstructor() configuration method, when the component is registered.

• reflection-based component registration does not currently support multiple constructors

Example usage (works with delegate-based registration):

var container = containerBuilder.Build();

Console.WriteLine(container.Resolve<TwoConstructors>(TypedParameter.From(container.Resolve<IA>())));
Console.WriteLine(container.Resolve<TwoConstructors>(TypedParameter.From(container.Resolve<IB>())));
Console.WriteLine(container.Resolve<TwoConstructors>()); // throws expected exception

Console.WriteLine(container.Resolve<Func<IA, TwoConstructors>>()(container.Resolve<IA>()));
Console.WriteLine(container.Resolve<Func<IB, TwoConstructors>>()(container.Resolve<IB>()));
Console.WriteLine(container.Resolve<Func<TwoConstructors>>()); // returns a func that will always throw the expected exception

[griffithtp]

+1

[zhangxin511]

+1. Should be very helpful