c# - Setting generic type at runtime

Question

I have a class

public class A<T>
{
   public static string B(T obj)
   {
       return TransformThisObjectToAString(obj);
   }
}

The use of string above is purely exemplary. I can call the static function like this just fine on a known/specified type:

string s= A<KnownType>.B(objectOfKnownType);

How do I make this call, if I don't know T beforehand, rather I have a variable of type Type that holds the type. If I do this:

Type t= typeof(string);
string s= A<t>.B(someStringObject);

I get this compiler error:

Cannot implicitly convert type 't' to 'object'

Answer 1

You can't do this directly, but you can use reflection to provide a type parameter of a class at run-time. I haven't tested this, but something like this should work:

// We want to do something like this:
//    object o = "Hello"
//    Type t = o.GetType(); 
//
// This is pseudo-code only:
//    string s = A<t>.B(o); 

string InvokeA(object o) {
  // Specify the type parameter of the A<> type
  Type genericType = typeof(A<>).MakeGenericType(new Type[] { o.GetType() });
  // Get the 'B' method and invoke it:
  object res = genericType.GetMethod("B").Invoke(new object[] { o });
  // Convert the result to string & return it
  return (string)res;
}

Of course, the question is if this is really what you need - If you don't know anything about the object given as an argument, you could as well write the whole code just using object. However, I can imagine some scenarios where this would be useful, so I guess you can try using this.