Andrew Peters’ Blog

Sometimes you are unable to use generics at the class level. For example, within Windows.Forms, using class-level generic arguments breaks the designer. One solution is to use what I call a “Generic Closure”. Basically, you can use a generic argument at the method level and then save a block that captures some usage of the generic type. E.g.

delegate object Creator(); 
 
Creator _newT;
 
void Foo<T>() 
  where T : new()
{ 
  _newT = delegate { return new T(); }
}
 
// then invoke the delegate sometime later:
 
object t = _newT();

In this example the generic closure serves two purposes:

1. It enforces a default public constructor.
2. It allows us to new up a T without resorting to reflection.

Obviously, being able to use class level generics in this context is preferable so lets hope it gets baked in completely some time soon.