Question: Registering Generic Singleton

[Mike-E-angelo]

Got another one for you. :)

Consider the following class:

sealed class Singleton<T> : ISource<T>
{
	public static Singleton<T> Default { get; } = new Singleton<T>();
	Singleton() {}

	public T Get() => default(T);
}

Up until now I have been using RegisterInstance with no problem. However, here the generics again add yet another wrinkle. What would be ideal is to have a Register(Type type, Func<IServiceFactory, object> factory) but there does not appear to be one, not that I can find at least. Is there a way to do something like this that I might be overlooking?

The other issue I have been running into is that I have tried RegisterFallback but it never reaches it because my constructor selector throws an exception when it cannot find any constructors on the above class (since it's private).

[seesharper]

The problem with Register(Type type, Func<IServiceFactory, object> is that you would have to look at the generic arguments of the service type and then use MakeGenericType inside that factory delegate to create the instance. You can also take a look at this issue where the exact same scenario is discussed

aspnet/DependencyInjection#474

When it comes to singletons it would probably be best register the class with the container using the PerContainerLifetime which is a singleton within the container instance. Unless you are dealing with multiple container instances that should cover your singleton needs 😄 In your case you don't really need Singleton<T>, just register T with the container with the PerContainerLifetime.

[Mike-E-angelo]

Ah, I tripped over my own suggestion. The call would look like such:

Register(Type type, Func<IServiceFactory, Type, object> factory) ... where LightInject would provide the generic type that has already been made.

I am indeed using PerContainerLifetime, everywhere. LOL. In the example above, it does look like I am passing an "instance" (set to default(T)), but really what I am registering is a ISource<T> (or some variant) which is itself a singleton, but not the objects in which it returns. If that makes any sense. 😄