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Subclass json_object so primitives shrink from 168 to 24 bytes

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The previous "every member in a struct" layout cost 168 bytes per
json_object, even for JSON_NULL / JSON_TRUE / JSON_FALSE nodes that
have no payload. Splitting json_object into a small base class plus
json_number / json_string / json_array / json_hash subclasses brings
each instance down to just the size of its actual contents:

  json_object (base, TRUE / FALSE / NULL)   24 bytes
  json_number                                48 bytes
  json_string                                48 bytes
  json_array  (empty)                        48 bytes
  json_hash   (empty)                        72 bytes

Other size wins along the way:

* Drop enable_shared_from_this<json_object> (its embedded weak_ptr
  was 16 bytes per node). json_pull now keeps an explicit
  container_stack and the parser no longer needs to resurrect a
  shared_ptr from a raw `parent` walk.
* Remove the unused `refcon` slot from the string variant.
* No virtual destructor: shared_ptr keeps the deleter from the
  original std::make_shared<json_xxx> call, so destroying a
  shared_ptr<json_object> still runs the right subclass dtor.

The base class exposes type-tagged accessors (o->string(),
o->number(), o->array(), o->keys(), o->values(), o->large_signed(),
o->large_unsigned()) that assert the type matches and downcast to
the appropriate subclass storage. All call sites were swept from
the old `o->value.X.Y` field paths to these accessors. A raw-pointer
overload of json_hash_get() replaces the few external uses of
shared_from_this() that survived in geojson-loop.cpp.

Co-authored-by: Cursor <cursoragent@cursor.com>
This commit is contained in:
Erica Fischer
2026-05-30 17:49:08 -07:00
co-authored by Cursor
parent 3da03c6075
commit f366b2c4aa
14 changed files with 424 additions and 291 deletions
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pmtiles_file.cpp
+12 -12
View File
@@ -415,37 +415,37 @@ sqlite3 *pmtilesmeta2tmp(const char *fname, const char *pmtiles_map) {
state.nospace = true;
state.json_write_hash();
for (size_t i = 0; i < o->value.object.keys.size(); i++) {
const std::string &key = o->value.object.keys[i]->value.string.string;
if (key == "vector_layers" && o->value.object.values[i]->type == JSON_ARRAY) {
for (size_t i = 0; i < o->keys().size(); i++) {
const std::string &key = o->keys()[i]->string();
if (key == "vector_layers" && o->values()[i]->type == JSON_ARRAY) {
has_json = true;
state.nospace = true;
state.json_write_string("vector_layers");
state.nospace = true;
state.json_write_json(json_stringify(o->value.object.values[i]));
} else if (key == "tilestats" && o->value.object.values[i]->type == JSON_HASH) {
state.json_write_json(json_stringify(o->values()[i]));
} else if (key == "tilestats" && o->values()[i]->type == JSON_HASH) {
has_json = true;
state.nospace = true;
state.json_write_string("tilestats");
state.nospace = true;
state.json_write_json(json_stringify(o->value.object.values[i]));
} else if (key == "strategies" && o->value.object.values[i]->type == JSON_ARRAY) {
sql = sqlite3_mprintf("INSERT INTO metadata (name, value) VALUES ('strategies', %Q);", json_stringify(o->value.object.values[i]).c_str());
state.json_write_json(json_stringify(o->values()[i]));
} else if (key == "strategies" && o->values()[i]->type == JSON_ARRAY) {
sql = sqlite3_mprintf("INSERT INTO metadata (name, value) VALUES ('strategies', %Q);", json_stringify(o->values()[i]).c_str());
if (sqlite3_exec(db, sql, NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "set %s in metadata: %s\n", key.c_str(), err);
}
sqlite3_free(sql);
} else if (key == "tippecanoe_decisions" && o->value.object.values[i]->type == JSON_HASH) {
sql = sqlite3_mprintf("INSERT INTO metadata (name, value) VALUES ('tippecanoe_decisions', %Q);", json_stringify(o->value.object.values[i]).c_str());
} else if (key == "tippecanoe_decisions" && o->values()[i]->type == JSON_HASH) {
sql = sqlite3_mprintf("INSERT INTO metadata (name, value) VALUES ('tippecanoe_decisions', %Q);", json_stringify(o->values()[i]).c_str());
if (sqlite3_exec(db, sql, NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "set %s in metadata: %s\n", key.c_str(), err);
}
sqlite3_free(sql);
} else if (o->value.object.keys[i]->type != JSON_STRING || o->value.object.values[i]->type != JSON_STRING) {
} else if (o->keys()[i]->type != JSON_STRING || o->values()[i]->type != JSON_STRING) {
fprintf(stderr, "%s\n", key.c_str());
fprintf(stderr, "%s: non-string in metadata\n", fname);
} else {
sql = sqlite3_mprintf("INSERT INTO metadata (name, value) VALUES (%Q, %Q);", key.c_str(), o->value.object.values[i]->value.string.string.c_str());
sql = sqlite3_mprintf("INSERT INTO metadata (name, value) VALUES (%Q, %Q);", key.c_str(), o->values()[i]->string().c_str());
if (sqlite3_exec(db, sql, NULL, NULL, &err) != SQLITE_OK) {
fprintf(stderr, "set %s in metadata: %s\n", key.c_str(), err);
}