Register partially open generic in simple injector

Question

I'm trying to register a open generic interface IService<T1> and to resolve it using the following partially open implementation class Service<T0, T1>. In this scenario, T0 would be fixed, and T1 from Service and IService would be the same.

Ideally, it would look something like this:

container.Register<IService<>, Service<ExplicitType,>>(Lifestyle.Singleton);

but that's incorrect c#.

My question is:

• does that make sense ? Or is there a better way. I would like to avoid making the class Service<ExplicitType,> if possible.
• is it even possible ?

I did not find the great documentation helpful on this matter.

Answer 1

This is certainly possible, but you can't express partially open generic types in C#. You will need to revert to Reflection. You can specify your partially open type as follows:

Type implementation =
    typeof(Service<,>).MakeGenericType(
        typeof(ExplicitType),
        typeof(Service<,>).GetGenericTypeArguments()[1]));

Registration in Simple Injector is now child's play:

container.Register(typeof(IService<>), implementation);

does that make sense?

Your example is very 'generic' (no pun intended) so it is hard to draw conclusions from that, but there are absolutely good use cases for partially open generic types. That's why Simple Injector has OOTB support for them.

I did not find the great documentation helpful on this matter.

The documentation actually has information about this, but in the documentation it is called "partially-closed", which is probably rhe reason you didn't find it.