Create instance of generic class with dynamic generic type parameter

Question

I need to create instance of a generic class like this:

 Type T = Type.GetType(className).GetMethod(functionName).ReturnType;
 var comparer = new MyComparer&         


        

Answer 1

I found very simple solution to problem. There is no need to cast object to specific type T, just use dynamic keyword instead of casting

   Type myGeneric = typeof(MyComparer<>);
   Type constructedClass = myGeneric.MakeGenericType(T);
   object created = Activator.CreateInstance(constructedClass);
   dynamic comparer = created; // No need to cast created object to T

and then I can use comparer normally to call its methods like:

   return comparer.Equals(myResultAsT, correctResultAsT);

According to LueTm comments, it is probably possible to use reflection again and call comparer methods, but this solution looks much easier.

Answer 2

Looks like you're almost there:

// t is a variable, so make it lowercase. This is where some of the confusion comes from
Type t = Type.GetType(className).GetMethod(functionName).ReturnType;
Type myGeneric = typeof(IEqualityComparer<>);

// You need to provide the generic type to make it generic with
// You want IEqualityComparer<T>, so:
Type constructedClass = myGeneric.MakeGenericType(t); 

// Now create the object
object created = Activator.CreateInstance(constructedClass);

// This is tricky without more context...
// You could try this, but to tell you more I would need to know where you use
// the comparer instance. Are you using it in a LINQ query, or in a Sort()?
// If so just cast it to a IEqualityComparer<YourType>, and
// make YourType whaterver you need it to be in the list or the query...
var comparer = (IEqualityComparer<object>)created;