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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
Download Patch File Download Diff File Expand all files Collapse all files
tile-join.cpp
+26 -26
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@@ -969,12 +969,12 @@ void handle_strategies(const unsigned char *s, std::vector<strategy> *st) {
json_object_ptr o = json_read_tree(jp);
if (o != nullptr && o->type == JSON_ARRAY) {
for (size_t i = 0; i < o->value.array.array.size(); i++) {
json_object_ptr h = o->value.array.array[i];
for (size_t i = 0; i < o->array().size(); i++) {
json_object_ptr h = o->array()[i];
if (h->type == JSON_HASH) {
for (size_t j = 0; j < h->value.object.keys.size(); j++) {
json_object_ptr k = h->value.object.keys[j];
json_object_ptr v = h->value.object.values[j];
for (size_t j = 0; j < h->keys().size(); j++) {
json_object_ptr k = h->keys()[j];
json_object_ptr v = h->values()[j];
if (k->type != JSON_STRING) {
fprintf(stderr, "Key %zu of %zu is not a string: %s\n", j, i, s);
@@ -985,25 +985,25 @@ void handle_strategies(const unsigned char *s, std::vector<strategy> *st) {
st->resize(i + 1);
}
const std::string &key = k->value.string.string;
const std::string &key = k->string();
if (key == "dropped_by_rate") {
(*st)[i].dropped_by_rate += v->value.number.number;
(*st)[i].dropped_by_rate += v->number();
} else if (key == "dropped_by_gamma") {
(*st)[i].dropped_by_gamma += v->value.number.number;
(*st)[i].dropped_by_gamma += v->number();
} else if (key == "dropped_as_needed") {
(*st)[i].dropped_as_needed += v->value.number.number;
(*st)[i].dropped_as_needed += v->number();
} else if (key == "coalesced_as_needed") {
(*st)[i].coalesced_as_needed += v->value.number.number;
(*st)[i].coalesced_as_needed += v->number();
} else if (key == "truncated_zooms") {
(*st)[i].truncated_zooms += v->value.number.number;
(*st)[i].truncated_zooms += v->number();
} else if (key == "detail_reduced") {
(*st)[i].detail_reduced += v->value.number.number;
(*st)[i].detail_reduced += v->number();
} else if (key == "tiny_polygons") {
(*st)[i].tiny_polygons += v->value.number.number;
(*st)[i].tiny_polygons += v->number();
} else if (key == "tile_size_desired") {
(*st)[i].tile_size += v->value.number.number;
(*st)[i].tile_size += v->number();
} else if (key == "feature_count_desired") {
(*st)[i].feature_count += v->value.number.number;
(*st)[i].feature_count += v->number();
}
}
}
@@ -1016,14 +1016,14 @@ void handle_strategies(const unsigned char *s, std::vector<strategy> *st) {
void handle_vector_layers(json_object_ptr vector_layers, std::map<std::string, layermap_entry> &layermap, std::map<std::string, std::string> &attribute_descriptions) {
if (vector_layers != nullptr && vector_layers->type == JSON_ARRAY) {
for (size_t i = 0; i < vector_layers->value.array.array.size(); i++) {
if (vector_layers->value.array.array[i]->type == JSON_HASH) {
json_object_ptr id = json_hash_get(vector_layers->value.array.array[i], "id");
json_object_ptr desc = json_hash_get(vector_layers->value.array.array[i], "description");
for (size_t i = 0; i < vector_layers->array().size(); i++) {
if (vector_layers->array()[i]->type == JSON_HASH) {
json_object_ptr id = json_hash_get(vector_layers->array()[i], "id");
json_object_ptr desc = json_hash_get(vector_layers->array()[i], "description");
if (id != nullptr && desc != nullptr && id->type == JSON_STRING && desc->type == JSON_STRING) {
const std::string &sid = id->value.string.string;
const std::string &sdesc = desc->value.string.string;
const std::string &sid = id->string();
const std::string &sdesc = desc->string();
if (sdesc.size() != 0) {
auto f = layermap.find(sid);
@@ -1033,17 +1033,17 @@ void handle_vector_layers(json_object_ptr vector_layers, std::map<std::string, l
}
}
json_object_ptr fields = json_hash_get(vector_layers->value.array.array[i], "fields");
json_object_ptr fields = json_hash_get(vector_layers->array()[i], "fields");
if (fields != nullptr && fields->type == JSON_HASH) {
for (size_t j = 0; j < fields->value.object.keys.size(); j++) {
if (fields->value.object.keys[j]->type == JSON_STRING && fields->value.object.values[j]->type) {
const std::string &desc2 = fields->value.object.values[j]->value.string.string;
for (size_t j = 0; j < fields->keys().size(); j++) {
if (fields->keys()[j]->type == JSON_STRING && fields->values()[j]->type) {
const std::string &desc2 = fields->values()[j]->string();
if (desc2 != "Number" &&
desc2 != "String" &&
desc2 != "Boolean" &&
desc2 != "Mixed") {
attribute_descriptions.insert(std::pair<std::string, std::string>(fields->value.object.keys[j]->value.string.string, desc2));
attribute_descriptions.insert(std::pair<std::string, std::string>(fields->keys()[j]->string(), desc2));
}
}
}