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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
read_json.cpp
+22 -22
View File
@@ -63,7 +63,7 @@ void parse_coordinates(int t, json_object_ptr j, drawvec &out, int op, const cha
int within = geometry_within[t];
if (within >= 0) {
size_t i;
for (i = 0; i < j->value.array.array.size(); i++) {
for (i = 0; i < j->array().size(); i++) {
if (within == GEOM_POINT) {
if (i == 0 || mb_geometry[t] == VT_POINT) {
op = VT_MOVETO;
@@ -72,16 +72,16 @@ void parse_coordinates(int t, json_object_ptr j, drawvec &out, int op, const cha
}
}
parse_coordinates(within, j->value.array.array[i], out, op, fname, line, feature);
parse_coordinates(within, j->array()[i], out, op, fname, line, feature);
}
} else {
if (j->value.array.array.size() >= 2 && j->value.array.array[0]->type == JSON_NUMBER && j->value.array.array[1]->type == JSON_NUMBER) {
if (j->array().size() >= 2 && j->array()[0]->type == JSON_NUMBER && j->array()[1]->type == JSON_NUMBER) {
long long x, y;
double lon = j->value.array.array[0]->value.number.number;
double lat = j->value.array.array[1]->value.number.number;
double lon = j->array()[0]->number();
double lat = j->array()[1]->number();
projection->project(lon, lat, 32, &x, &y);
if (j->value.array.array.size() > 2) {
if (j->array().size() > 2) {
static int warned = 0;
if (!warned) {
@@ -129,7 +129,7 @@ serial_val stringify_value(json_object_ptr value, const char *reading, int line,
if (vt == JSON_STRING) {
sv.type = mvt_string;
sv.s = value->value.string.string;
sv.s = value->string();
std::string err = check_utf8(sv.s);
if (err.size() > 0) {
@@ -140,12 +140,12 @@ serial_val stringify_value(json_object_ptr value, const char *reading, int line,
} else if (vt == JSON_NUMBER) {
sv.type = mvt_double;
if (value->value.number.large_unsigned != 0) {
sv.s = std::to_string(value->value.number.large_unsigned);
} else if (value->value.number.large_signed != 0) {
sv.s = std::to_string(value->value.number.large_signed);
if (value->large_unsigned() != 0) {
sv.s = std::to_string(value->large_unsigned());
} else if (value->large_signed() != 0) {
sv.s = std::to_string(value->large_signed());
} else {
sv.s = milo::dtoa_milo(value->value.number.number);
sv.s = milo::dtoa_milo(value->number());
}
} else if (vt == JSON_TRUE) {
sv.type = mvt_bool;
@@ -200,12 +200,12 @@ std::pair<int, drawvec> parse_geometry(json_object_ptr geometry, json_pull_ptr j
int t;
for (t = 0; t < GEOM_TYPES; t++) {
if (geometry_type->value.string.string == geometry_names[t]) {
if (geometry_type->string() == geometry_names[t]) {
break;
}
}
if (t >= GEOM_TYPES) {
fprintf(stderr, "Filter output:%d: Can't handle geometry type %s: ", jp->line, geometry_type->value.string.string.c_str());
fprintf(stderr, "Filter output:%d: Can't handle geometry type %s: ", jp->line, geometry_type->string().c_str());
json_context(j);
exit(EXIT_JSON);
}
@@ -325,7 +325,7 @@ std::vector<mvt_layer> parse_layers(FILE *fp, int z, unsigned x, unsigned y, int
if (type == nullptr || type->type != JSON_STRING) {
continue;
}
if (type->value.string.string != "Feature") {
if (type->string() != "Feature") {
continue;
}
@@ -342,7 +342,7 @@ std::vector<mvt_layer> parse_layers(FILE *fp, int z, unsigned x, unsigned y, int
if (tippecanoe != nullptr) {
layer = json_hash_get(tippecanoe, "layer");
if (layer != nullptr && layer->type == JSON_STRING) {
layername = layer->value.string.string;
layername = layer->string();
}
}
@@ -375,22 +375,22 @@ std::vector<mvt_layer> parse_layers(FILE *fp, int z, unsigned x, unsigned y, int
json_object_ptr id = json_hash_get(j, "id");
if (id != nullptr && id->type == JSON_NUMBER) {
feature.id = id->value.number.number;
if (id->value.number.large_unsigned > 0) {
feature.id = id->value.number.large_unsigned;
feature.id = id->number();
if (id->large_unsigned() > 0) {
feature.id = id->large_unsigned();
}
feature.has_id = true;
}
for (size_t i = 0; i < properties->value.object.keys.size(); i++) {
serial_val sv = stringify_value(properties->value.object.values[i], "Filter output", jp->line, j);
for (size_t i = 0; i < properties->keys().size(); i++) {
serial_val sv = stringify_value(properties->values()[i], "Filter output", jp->line, j);
// Nulls can be excluded here because this is the postfilter
// and it is nearly time to create the vector representation
if (sv.type != mvt_null) {
mvt_value v = stringified_to_mvt_value(sv.type, sv.s.c_str(), tile_stringpool);
l->second.tag(feature, properties->value.object.keys[i]->value.string.string, v);
l->second.tag(feature, properties->keys()[i]->string(), v);
}
}