On Tue, 23 Jun 2020 11:18:37 +0200
Victor Stinner <vstin...@python.org> wrote:
>
> Pseudo-code:
>
> void iterate(PyObject *obj)
> {
> PyObjectPP_View view;
>
> if (PyObjectPP_View_Get(&view, obj)) {
> // fast-path: the object provides a PyObject** view
> for (Py_ssize_t i=0; i < view.len; i++ {
> PyObject *item = view.array[i];
> ...
> }
> PyObjectPP_View_Release(&view);
> }
> else {
> // slow code path using PySequence_GetItem() or anything else
> ...
> }
It is quite cumbersome for extension code to have to re-implement all
this by hand. Instead, it would be nice to have a "Visit" primitive so
that one can write e.g.:
void iterate(PyObject* obj)
{
Py_VisitObjectSequence([&](PyObject* item) {
// ...
});
}
The above is a C++ lambda function (a closure, actually). The C
spelling would be less nice, and you'd have to ensure that it is still
performant (i.e., that the visitor is inlined inside the iteration
loop - at least in release builds).
(I called it Py_VisitObjectSequence so that you can also have
Py_VisitIntSequence, Py_VisitFloatSequence, etc.)
Regards
Antoine.
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