How can we put a variant message ( one of a few message types ) inside a protobuf message?

Question

How can we put a variant message ( one of a few message types ) inside a protobuf message?

message typeA {
    ....
}

message typeB {
    ....
}

message ty         


        

Answer 1

Check out the new oneof feature in version 2.6: https://developers.google.com/protocol-buffers/docs/reference/java-generated#oneof

You can now do something like this:

message TypeC {
    oneof oneof_name {
        TypeA a = 1;
        TypeB b = 2;
    }
}

Fields in the same oneof will share memory and only one field can be set at the same time.