TopOfBook# struct TopOfBook# Update relating to top of book (aggregate price) Public Members uint16_t stream_id = {}# Stream identifier. std::string_view exchange# Exchange. std::string_view symbol# Symbol. Layer layer# Top of book. UpdateType update_type = {}# Update type. std::chrono::nanoseconds exchange_time_utc = {}# Exchange timestamp, possibly from matching engine (UTC) uint64_t exchange_sequence = {}# Exchange message sequence number. std::chrono::nanoseconds sending_time_utc = {}# Exchange sending timestamp (UTC)