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Niels Lohmann
1df1e8a845
* Make cross-string-type basic_json conversion explicit without implicit conversions The converting constructor from another basic_json specialization was always implicit, so a value with a different string_t (std::wstring, a string with a custom allocator, ...) silently converted into a temporary, e.g. when passed to a function taking const nlohmann::json&. Such conversions do not produce correct values (#3425), and JSON_USE_IMPLICIT_CONVERSIONS=0 did not catch them. When JSON_USE_IMPLICIT_CONVERSIONS is 0, the constructor is now explicit if the string types differ. Specializations sharing a string type (json and ordered_json, different serializers or object maps) stay implicitly convertible, so the NLOHMANN_DEFINE_TYPE_* macros keep working with nested json members. get<BasicJsonType>() constructs explicitly and works in both modes. Fixes #2649. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Construct explicitly in get_to() and to_json(std::optional) With JSON_USE_IMPLICIT_CONVERSIONS=0 the conversion from a basic_json with a different string type is now explicit, but two library paths still assigned such a value implicitly and failed to compile inside the library: - get_to() with a basic_json target (the #2175 overload) did `v = *this`, so json(42).get_to(alt_json&) broke although get<alt_json>() works. - to_json(BasicJsonType&, const std::optional<T>&) is constrained on std::is_constructible (which accepts the explicit constructor) but did `j = *opt`, so converting a std::optional<alt_json> into a json broke. Both now construct the value explicitly, as get_impl() already does. Also replace static_cast<bool>(JSON_USE_IMPLICIT_CONVERSIONS) with a comparison: clang-tidy's modernize-use-bool-literals rejected the cast of the integer literal the macro expands to, failing ci_clang_tidy. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>