Remove mp_obj_type_t.methods entry and use .locals_dict instead.

Originally, .methods was used for methods in a ROM class, and
locals_dict for methods in a user-created class.  That distinction is
unnecessary, and we can use locals_dict for ROM classes now that we have
ROMable maps.

This removes an entry in the bloated mp_obj_type_t struct, saving a word
for each ROM object and each RAM object.  ROM objects that have a
methods table (now a locals_dict) need an extra word in total (removed
the methods pointer (1 word), no longer need the sentinel (2 words), but
now need an mp_obj_dict_t wrapper (4 words)).  But RAM objects save a
word because they never used the methods entry.

Overall the ROM usage is down by a few hundred bytes, and RAM usage is
down 1 word per user-defined type/class.

There is less code (no need to check 2 tables), and now consistent with
the way ROM modules have their tables initialised.

Efficiency is very close to equivaluent.

1 files changed, 8 insertions, 6 deletions

diff --git a/stm/file.c b/stm/file.c
index e56b05fae..208ce804b 100644
--- a/stm/file.c
+++ b/stm/file.c
@@ -5,6 +5,7 @@
 #include "mpconfig.h"
 #include "qstr.h"
 #include "obj.h"
+#include "map.h"
 #include "file.h"
 #include "ff.h"
 
@@ -52,18 +53,19 @@ static MP_DEFINE_CONST_FUN_OBJ_1(file_obj_close_obj, file_obj_close);
 
 // TODO gc hook to close the file if not already closed
 
-static const mp_method_t file_methods[] = {
-    { MP_QSTR_read, &file_obj_read_obj },
-    { MP_QSTR_write, &file_obj_write_obj },
-    { MP_QSTR_close, &file_obj_close_obj },
-    { MP_QSTR_NULL, NULL },
+STATIC const mp_map_elem_t file_locals_dict_table[] = {
+    { MP_OBJ_NEW_QSTR(MP_QSTR_read), (mp_obj_t)&file_obj_read_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_write), (mp_obj_t)&file_obj_write_obj },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_close), (mp_obj_t)&file_obj_close_obj },
 };
 
+STATIC MP_DEFINE_CONST_DICT(file_locals_dict, file_locals_dict_table);
+
 static const mp_obj_type_t file_obj_type = {
     { &mp_type_type },
     .name = MP_QSTR_File,
     .print = file_obj_print,
-    .methods = file_methods,
+    .locals_dict = (mp_obj_t)&file_locals_dict,
 };
 
 mp_obj_t pyb_io_open(mp_obj_t o_filename, mp_obj_t o_mode) {