MAINT: Refactor UFunc core to use NEP 43 style dispatching/promotion

The first (big) chunk of a multi-step process to update all ufuncs
to NEP 43 style ufuncs.

This limits itself to normal ufunc calls and sets ufunc.at and
all reduce-like operations to the side.  These would add another
level of complexity.

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/source/reference/c-api/types-and-structures.rst b/doc/source/reference/c-api/types-and-structures.rst
index 75a97c20e..43d1eccb7 100644
--- a/doc/source/reference/c-api/types-and-structures.rst
+++ b/doc/source/reference/c-api/types-and-structures.rst
@@ -818,6 +818,7 @@ PyUFunc_Type and PyUFuncObject
           npy_intp *core_dim_sizes;
           npy_uint32 *core_dim_flags;
           PyObject *identity_value;
+          /* Further private slots (size depends on the NumPy version) */
       } PyUFuncObject;
 
    .. c:macro: PyObject_HEAD
@@ -957,6 +958,12 @@ PyUFunc_Type and PyUFuncObject
 
    .. c:member:: PyUFunc_LegacyInnerLoopSelectionFunc *legacy_inner_loop_selector
 
+       .. note::
+
+            Some fallback support for this slot exists, but it should not be
+            called and not be used in the future.
+            See ref:`NEP 41 <NEP41>` and ref:`NEP 43 <NEP43>`
+
        A function which returns an inner loop. The ``legacy`` in the name arises
        because for NumPy 1.6 a better variant had been planned. This variant
        has not yet come about.