Niels Lohmann 43afb5bebc Do not instantiate a hash map with an incomplete basic_json in the tests ...

object_t is probed for key_compare inside the definition of basic_json, so
it is instantiated while basic_json is still incomplete. Whether a hash map
survives that depends on the standard library: libstdc++ 9 needs the size of
the mapped type to instantiate std::unordered_map's node type and rejects
the adapter, which broke the GCC 9 builds.

The test now derives its no-key_compare object type from std::map -- which
does cope -- and shadows the inherited key_compare member type with an
entity that is not a type, so the library's probe finds none, exactly as for
a hash map. The unflatten() order-independence checks in unit-json_pointer
already cover the behaviour that the unordered object type was there for.
The limitation is documented for std::unordered_map.

Also address two Clang-Tidy findings the earlier commits introduced:
erase_from_object() declares its iterator with auto, and at(size_type) checks
the type first and then falls through to the return instead of throwing from
an else branch.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-08-28 18:17:15 +00:00

..

json_fwd.hpp

📄 adjust year (#5044)

2026-01-01 20:00:39 +01:00

json.hpp

Do not instantiate a hash map with an incomplete basic_json in the tests

2026-08-28 18:17:15 +00:00