Does Protocol Buffers support move constructor

Question

I've checked the move constructor spec and a Message constructor source and didn't find one.

If there's not, does anyone know about a plan to add it?

I'm using proto3 syntax, writing a library and considering between return through value vs unique_ptr.

Answer 1

According to https://github.com/google/protobuf/issues/2791 this will be supported in Protobuf version 3.4.0.

Answer 2

1. If you try to use a assignment operator, RVO will do optimization to prevent an extra copy.

   // RVO will bring the return value to a without using copy constructor.
   SomeMessage a = SomeFooWithMessageReturned();
   

2. If you want to use std::move to move a lvalue into a list/sub message, etc. Try to use ConcreteMessage::Swap method. The swapped item will be useless.

   // Non-copy usage.
   somemessage.add_somerepeated_message()->Swap(&a);
   somemessage.mutable_somesinglar_message()->Swap(&a);
   // With message copying
   somemessage.add_somerepeated_message()->CopyFrom(a);
   *somemessage.mutable_somesinglar_message() = a;