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Niels Lohmann
6be8c2e986
copy_object_level(), used by the copy constructor and copy assignment once a value is nested deeper than the iterative deep copy's bound (128 levels, or every copy under JSON_NO_THREAD_LOCAL), built each object's copy with the object type's plain range constructor. That default-constructs the object's comparator instead of copying the original's. For an object type whose comparator carries state, such as a std::map that compares keys case-sensitively only when constructed that way, the copy then ordered - and could even deduplicate - its keys differently from the original. Add detail::is_comparator_constructible_object_type, a detection trait for object types that provide a key_comp() and a constructor taking a range and a comparator, the way std::map does. copy_object_level now dispatches on it: an object type that qualifies gets its copy built with src_object.key_comp() passed along; other object types, such as nlohmann::ordered_map (which has a key_compare for its std::map-like interface, but no key_comp()), keep using the plain range constructor exactly as before. merge_patch and update() were checked for the same pattern; neither is affected, since both only ever add members one at a time to an object that already has its own comparator (or start a brand new default-constructed one), rather than rebuilding an object_t from a range copied out of an existing, possibly custom-comparator object. Fixes #5649. Signed-off-by: Niels Lohmann <mail@nlohmann.me>