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Json: implement structural == for JsonObject/JsonValue/JsonArray - #1560
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Replaces the TODO in JsonObject.h where operator== compared dump()
strings (two full JSON serializations and string allocations per
compare). The new operators compare types and contents recursively:
- JsonValue: type-strict, then primitive/pointer payload compare.
- JsonArray: size, then element-wise.
- JsonObject: size, then key/value pairs (std::map iteration order).
Semantics match the old dump-based == for all well-formed values
(int 1 != 1.0, key order irrelevant), with one deliberate fix:
null != {} — the old compare treated them as equal because
to_nlohmann() serializes an empty object as null (pre-existing
dump bug, tracked separately).
Mysticial
approved these changes
Oct 11, 2026
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Resolves the TODO at
Common/Cpp/Json/JsonObject.h:22("implement == properly. For JsonValue as well.").What
Replaces the
dump()-string comparison with real structural==/!=for all three JSON types:JsonValue(JsonValue.h,JsonValue.cpp) — type-strict, then compares the payload: primitives directly, and recursively for string/array/object.JsonArray(JsonArray.h) — size, then element-wise.JsonObject(JsonObject.h) — size, then key/value pairs (map iteration order).JsonValue::operator==is declared as a friend in the header and defined inJsonValue.cpp, because it needs the complete types ofJsonArray/JsonObject.Why
The old
JsonObject::operator==didx.dump() == y.dump(): two full JSON serializations (nlohmann round-trip + allocation) per comparison. The new operators do a cheap recursive structural compare.Semantics
Matches the old dump-based behavior for all well-formed values — type-strict (
int 1 != 1.0, since they dump as"1"vs"1.0"), key-order independent. One deliberate correction:null != {}. The old compare treated them as equal because of a pre-existing serialization bug:to_nlohmann()(JsonTools.cpp:31) returns a nullnlohmann::jsonfor an empty object, so an empty objectdump()s as"null"instead of"{}". The new==correctly treats them as different. (Thedump()bug itself is left alone — separate concern, happy to fix in a follow-up.)Verification
g++ -std=c++23 -Wall -Wextra -fsyntax-onlyclean on all four Json TUs plus a couple of consumer TUs.!=, and a cross-check of new vs old equality across ~210 pairs — identical everywhere except the twonull/{}cases above, where the new behavior is the correct one.