[Numpy-discussion] Is it OK to extend the ndarray structure?

[Sebastian Berg]

Hi all,

just curious, has anyone reservations about extending the ndarray
struct (and the void scalar one)?

The reason is that, I am starting to dislike the way we handle the
buffer interface.
Due to issues with backward compatibility, we cannot use the "right"
way to free the buffer information. Because of that, the way we solve
it is by storing lists of pointers in a dictionary...

To me this seems a bit complicating, and is annoying since it adds a
dictionary lookup overhead to every single array deletion (and
inserting for every buffer creation). Also, it looks a bit like a
memory leak in some cases (although that probably only annoys me and
only when running valgrind).

It seems that it would be much simpler to tag the buffer-info on to the
array object itself. Which, however, would require extending the array
object by a single pointer [1].

Extending is in theory an ABI break if anyone subclasses ndarray from C
(extending the struct) and does not very carefully anticipate the
possibility.  I am not even sure we support that, but its hard to be
sure...

Cheers,

Sebastian


[1] The size difference should not matter IMO, and with cythons
memoryviews buffers are not an uncommon feature in any case, for the
void scalar it is a bit bigger, but they are also very rare. 
(I thought of using weak references, but the CPython API seems not very
fleshed out, or at least not documented, so not sure about that).