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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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attribute.cpp
+4 -4
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@@ -55,9 +55,9 @@ void set_attribute_accum(std::unordered_map<std::string, attribute_op> &attribut
exit(EXIT_JSON);
}
for (size_t i = 0; i < o->value.object.keys.size(); i++) {
json_object_ptr k = o->value.object.keys[i];
json_object_ptr v = o->value.object.values[i];
for (size_t i = 0; i < o->keys().size(); i++) {
json_object_ptr k = o->keys()[i];
json_object_ptr v = o->values()[i];
if (k->type != JSON_STRING) {
fprintf(stderr, "%s: -E%s: key %zu not a string\n", *argv, arg, i);
@@ -68,7 +68,7 @@ void set_attribute_accum(std::unordered_map<std::string, attribute_op> &attribut
exit(EXIT_JSON);
}
set_attribute_accum(attribute_accum, k->value.string.string.c_str(), v->value.string.string.c_str());
set_attribute_accum(attribute_accum, k->string().c_str(), v->string().c_str());
}
return;