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.

Well that is very disappointing news.

Even the decoder makes a copy even though it's returning a string_view? What's the point then.

I can understand encoders having to make copies, but not in a decoder.