A Resource is a type where its memory is controlled by SDL, usually with functions like SDL_Create*() and SDL_Destroy*().

To represent this type, we create RAII class where the Create* functions become its constructors and the Destroy is called by the destructor. Special *Ref exist to ease the use and allow flexibility on lifetime handling. Eg, for refcount'ed structs like SDL_Surface we get:

Surface: the main class, with all wrapped methods inside it. Copying an object of it increments the refcount field. The surface is destroyed when the last instance goes out of scope.
SurfaceRef, SurfaceConstRef: wrappers to allow interchangeable use of raw SDL_Surface and Surface as parameter.

For an opaque or non-refcounted type such as SDL_Window e get:

Window: the main class, with all wrapped methods inside it. Copying it disallowed. When the instance goes out of scope it destroy the window.
WindowRef: a wrapper to allow interchangeable use of raw SDL_Window and Window and WindowRef as parameter.