- Inconsistent id() vs direct access use in generated code

  The same for version().

? Move change_callback out of image

  We incur a bit of overhead in case of a batch (e.g., ~80KB for
  a batch size of 5000 on 64-bit) since we don't use this callback
  in all but the first element.

  The idea is to move it to the object statements, however, there
  are several places that need to access it that only got the image
  (e.g., init(image)). Storing a pointer in the image doesn't make
  sense since the struct itself is two pointers.

  So it is not clear this is worth the effort. See also a separate
  paper with some more thoughts on this.