Function concat

examples/server/json.hpp:4277–4283

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

}  // namespace detail
NLOHMANN_JSON_NAMESPACE_END