Function concat

extern/json/json.hpp:4281–4287

template<typename OutStringType = std::string, typename... Args>
inline OutStringType concat(Args && ... args)
{
    OutStringType str;
    str.reserve(concat_length(args...));
    concat_into(str, std::forward<Args>(args)...);
    return str;
}

}  // namespace detail
NLOHMANN_JSON_NAMESPACE_END