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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
plugin.cpp
+14 -14
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@@ -168,7 +168,7 @@ serial_feature parse_feature(json_pull_ptr jp, int z, unsigned x, unsigned y, st
if (type == nullptr || type->type != JSON_STRING) {
continue;
}
if (type->value.string.string != "Feature") {
if (type->string() != "Feature") {
continue;
}
@@ -208,12 +208,12 @@ serial_feature parse_feature(json_pull_ptr jp, int z, unsigned x, unsigned y, st
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);
}
@@ -252,22 +252,22 @@ serial_feature parse_feature(json_pull_ptr jp, int z, unsigned x, unsigned y, st
if (tippecanoe != nullptr) {
json_object_ptr layer = json_hash_get(tippecanoe, "layer");
if (layer != nullptr && layer->type == JSON_STRING) {
layername = layer->value.string.string;
layername = layer->string();
}
json_object_ptr index = json_hash_get(tippecanoe, "index");
if (index != nullptr && index->type == JSON_NUMBER) {
sf.index = index->value.number.number;
sf.index = index->number();
}
json_object_ptr sequence = json_hash_get(tippecanoe, "sequence");
if (sequence != nullptr && sequence->type == JSON_NUMBER) {
sf.seq = sequence->value.number.number;
sf.seq = sequence->number();
}
json_object_ptr extent = json_hash_get(tippecanoe, "extent");
if (extent != nullptr && extent->type == JSON_NUMBER) {
sf.extent = extent->value.number.number;
sf.extent = extent->number();
}
json_object_ptr dropped = json_hash_get(tippecanoe, "dropped");
@@ -297,9 +297,9 @@ serial_feature parse_feature(json_pull_ptr jp, int z, unsigned x, unsigned y, st
json_object_ptr id = json_hash_get(j, "id");
if (id != nullptr && id->type == JSON_NUMBER) {
sf.id = id->value.number.number;
if (id->value.number.large_unsigned > 0) {
sf.id = id->value.number.large_unsigned;
sf.id = id->number();
if (id->large_unsigned() > 0) {
sf.id = id->large_unsigned();
}
sf.has_id = true;
}
@@ -343,18 +343,18 @@ serial_feature parse_feature(json_pull_ptr jp, int z, unsigned x, unsigned y, st
}
}
for (size_t i = 0; i < properties->value.object.keys.size(); i++) {
serial_val v = stringify_value(properties->value.object.values[i], "Filter output", jp->line, j);
for (size_t i = 0; i < properties->keys().size(); i++) {
serial_val v = stringify_value(properties->values()[i], "Filter output", jp->line, j);
// Nulls can be excluded here because the expression evaluation filter
// would have already run before prefiltering
if (v.type != mvt_null) {
sf.full_keys.push_back(key_pool.pool(properties->value.object.keys[i]->value.string.string));
sf.full_keys.push_back(key_pool.pool(properties->keys()[i]->string()));
sf.full_values.push_back(v);
if (!postfilter) {
add_to_tilestats(ts->second.tilestats, properties->value.object.keys[i]->value.string.string, v);
add_to_tilestats(ts->second.tilestats, properties->keys()[i]->string(), v);
}
}
}