py/obj: Merge getiter and iternext mp_obj_type_t slots.

The goal here is to remove a slot (making way to turn make_new into a slot)
as well as reduce code size by the ~40 references to mp_identity_getiter
and mp_stream_unbuffered_iter.

This introduces two new type flags:
- MP_TYPE_FLAG_ITER_IS_ITERNEXT: This means that the "iter" slot in the
  type is "iternext", and should use the identity getiter.
- MP_TYPE_FLAG_ITER_IS_CUSTOM: This means that the "iter" slot is a pointer
  to a mp_getiter_iternext_custom_t instance, which then defines both
  getiter and iternext.

And a third flag that is the OR of both, MP_TYPE_FLAG_ITER_IS_STREAM: This
means that the type should use the identity getiter, and
mp_stream_unbuffered_iter as iternext.

Finally, MP_TYPE_FLAG_ITER_IS_GETITER is defined as a no-op flag to give
the default case where "iter" is "getiter".

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

Author: jimmo

examples/natmod/btree/btree_c.c

@@ -95,6 +95,7 @@ int mp_stream_posix_fsync(void *stream) {
 }
 
 mp_obj_full_type_t btree_type;
+mp_getiter_iternext_custom_t btree_getiter_iternext;
 
 #include "extmod/modbtree.c"
 
@@ -122,13 +123,16 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(btree_open_obj, 5, 5, btree_open);
 mp_obj_t mpy_init(mp_obj_fun_bc_t *self, size_t n_args, size_t n_kw, mp_obj_t *args) {
     MP_DYNRUNTIME_INIT_ENTRY
 
+    btree_getiter_iternext.getiter = btree_getiter;
+    btree_getiter_iternext.iternext = btree_iternext;
+
     btree_type.base.type = (void*)&mp_fun_table.type_type;
+    btree_type.flags = MP_TYPE_FLAG_ITER_IS_CUSTOM;
     btree_type.name = MP_QSTR_btree;
     MP_OBJ_TYPE_SET_SLOT(&btree_type, print, btree_print, 0);
-    MP_OBJ_TYPE_SET_SLOT(&btree_type, getiter, btree_getiter, 1);
-    MP_OBJ_TYPE_SET_SLOT(&btree_type, iternext, btree_iternext, 2);
-    MP_OBJ_TYPE_SET_SLOT(&btree_type, binary_op, btree_binary_op, 3);
-    MP_OBJ_TYPE_SET_SLOT(&btree_type, subscr, btree_subscr, 4);
+    MP_OBJ_TYPE_SET_SLOT(&btree_type, iter, &btree_getiter_iternext, 1);
+    MP_OBJ_TYPE_SET_SLOT(&btree_type, binary_op, btree_binary_op, 2);
+    MP_OBJ_TYPE_SET_SLOT(&btree_type, subscr, btree_subscr, 3);
     btree_locals_dict_table[0] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_close), MP_OBJ_FROM_PTR(&btree_close_obj) };
     btree_locals_dict_table[1] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_flush), MP_OBJ_FROM_PTR(&btree_flush_obj) };
     btree_locals_dict_table[2] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_get), MP_OBJ_FROM_PTR(&btree_get_obj) };
@@ -137,7 +141,7 @@ mp_obj_t mpy_init(mp_obj_fun_bc_t *self, size_t n_args, size_t n_kw, mp_obj_t *a
     btree_locals_dict_table[5] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_keys), MP_OBJ_FROM_PTR(&btree_keys_obj) };
     btree_locals_dict_table[6] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_values), MP_OBJ_FROM_PTR(&btree_values_obj) };
     btree_locals_dict_table[7] = (mp_map_elem_t){ MP_OBJ_NEW_QSTR(MP_QSTR_items), MP_OBJ_FROM_PTR(&btree_items_obj) };
-    MP_OBJ_TYPE_SET_SLOT(&btree_type, locals_dict, (void*)&btree_locals_dict, 5);
+    MP_OBJ_TYPE_SET_SLOT(&btree_type, locals_dict, (void*)&btree_locals_dict, 4);
 
     mp_store_global(MP_QSTR__open, MP_OBJ_FROM_PTR(&btree_open_obj));
     mp_store_global(MP_QSTR_INCL, MP_OBJ_NEW_SMALL_INT(FLAG_END_KEY_INCL));

extmod/modbtree.c

@@ -319,15 +319,19 @@ STATIC const mp_rom_map_elem_t btree_locals_dict_table[] = {
 
 STATIC MP_DEFINE_CONST_DICT(btree_locals_dict, btree_locals_dict_table);
 
+STATIC const mp_getiter_iternext_custom_t btree_getiter_iternext = {
+    .getiter = btree_getiter,
+    .iternext = btree_iternext,
+};
+
 STATIC MP_DEFINE_CONST_OBJ_TYPE(
     btree_type,
     MP_QSTR_btree,
-    MP_TYPE_FLAG_NONE,
+    MP_TYPE_FLAG_ITER_IS_CUSTOM,
     MP_TYPE_NULL_MAKE_NEW,
     // Save on qstr's, reuse same as for module
     print, btree_print,
-    getiter, btree_getiter,
-    iternext, btree_iternext,
+    iter, &btree_getiter_iternext,
     binary_op, btree_binary_op,
     subscr, btree_subscr,
     locals_dict, &btree_locals_dict