When working on my license project, I came across an uncommon case in C# where I would have to create an instance of a generic type (wich had multiple type parameters) dynamically.

Basically I had an instance of Dispatcher<A, B, C> that would be created with different type parameters A, B and C depending on the user’s selection. A and B were in my case classes of type ILoadBalancer and C a IScriptAssembler.

In order to avoid 3×3 Ifs in the code (which is actually quite dumb) I had to:

1. Extract an simple (not generic) interface IDispatcher from Dispatcher<A, B, C> class.
2. Instantiate the generic class at runtime:

   Type dynamicDispatcher = typeof(Dispatcher<,,>).MakeGenericType(
       new Type[] {typeof(CSharpScriptAssembler), userLocalBalancer, 
           userRemoteBalancer }
   );
   

3. Create a new instance of the newly generated non-generic type:

   m_Dispatcher = (IDispatcher)Activator.CreateInstance(
       dynamicDispatcher,
       new Object[] { userQueueSize, userNumberOfThreads, mode }
   );
   

So, as you can see, we have to first create a non-generic type out of the generic one at runtime. And then use the Activator singleton to actually create a new instance of that type.

Points of interest:

1. Type.MakeGenericType()
2. Activator.CreateInstance()