Those field accessors take and return string_view but they still copy. The official C++ library always owns the data internally and never aliases except in one

Those field accessors take and return string_view but they still copy. The official C++ library always owns the data internally and never aliases except in one niche use case: the field type is Cord, the input is large and meets some other criteria, and the caller had used kParseWithAliasing, which is undocumented. To a very close approximation you can say that the official protobuf C++ library always copies and owns strings.