py/objdict: Add mp_const_empty_dict_obj, use it for mp_const_empty_map.

py/map.c

@@ -40,17 +40,6 @@
 #define DEBUG_printf(...) (void)0
 #endif
 
-// Fixed empty map. Useful when need to call kw-receiving functions
-// without any keywords from C, etc.
-const mp_map_t mp_const_empty_map = {
-    .all_keys_are_qstrs = 0,
-    .is_fixed = 1,
-    .is_ordered = 1,
-    .used = 0,
-    .alloc = 0,
-    .table = NULL,
-};
-
 // This table of sizes is used to control the growth of hash tables.
 // The first set of sizes are chosen so the allocation fits exactly in a
 // 4-word GC block, and it's not so important for these small values to be

py/obj.h

@@ -422,8 +422,6 @@ typedef enum _mp_map_lookup_kind_t {
     MP_MAP_LOOKUP_ADD_IF_NOT_FOUND_OR_REMOVE_IF_FOUND = 3, // only valid for mp_set_lookup
 } mp_map_lookup_kind_t;
 
-extern const mp_map_t mp_const_empty_map;
-
 static inline bool mp_map_slot_is_filled(const mp_map_t *map, size_t pos) {
     assert(pos < map->alloc);
     return (map)->table[pos].key != MP_OBJ_NULL && (map)->table[pos].key != MP_OBJ_SENTINEL;
@@ -685,17 +683,22 @@ extern const struct _mp_obj_bool_t mp_const_false_obj;
 extern const struct _mp_obj_bool_t mp_const_true_obj;
 #endif
 
-// Constant objects, globally accessible: b'', (), Ellipsis, NotImplemented, GeneratorExit()
+// Constant objects, globally accessible: b'', (), {}, Ellipsis, NotImplemented, GeneratorExit()
 // The below macros are for convenience only.
 #define mp_const_empty_bytes (MP_OBJ_FROM_PTR(&mp_const_empty_bytes_obj))
 #define mp_const_empty_tuple (MP_OBJ_FROM_PTR(&mp_const_empty_tuple_obj))
 #define mp_const_notimplemented (MP_OBJ_FROM_PTR(&mp_const_notimplemented_obj))
 extern const struct _mp_obj_str_t mp_const_empty_bytes_obj;
 extern const struct _mp_obj_tuple_t mp_const_empty_tuple_obj;
+extern const struct _mp_obj_dict_t mp_const_empty_dict_obj;
 extern const struct _mp_obj_singleton_t mp_const_ellipsis_obj;
 extern const struct _mp_obj_singleton_t mp_const_notimplemented_obj;
 extern const struct _mp_obj_exception_t mp_const_GeneratorExit_obj;
 
+// Fixed empty map. Useful when calling keyword-receiving functions
+// without any keywords from C, etc.
+#define mp_const_empty_map (mp_const_empty_dict_obj.map)
+
 // General API for objects
 
 // These macros are derived from more primitive ones and are used to

py/objdict.c

@@ -33,6 +33,18 @@
 #include "py/objtype.h"
 #include "py/objstr.h"
 
+const mp_obj_dict_t mp_const_empty_dict_obj = {
+    .base = { .type = &mp_type_dict },
+    .map = {
+        .all_keys_are_qstrs = 0,
+        .is_fixed = 1,
+        .is_ordered = 1,
+        .used = 0,
+        .alloc = 0,
+        .table = NULL,
+    }
+};
+
 STATIC mp_obj_t dict_update(size_t n_args, const mp_obj_t *args, mp_map_t *kwargs);
 
 // This is a helper function to iterate through a dictionary.  The state of