Protocol buffers support oneof, which is a union type. https://developers.google.com/protocol-buffers/docs/proto#oneof https://developers.google.com/protocol-b

Protocol buffers support oneof, which is a union type. https://developers.google.com/protocol-buffers/docs/proto#oneof https://developers.google.com/protocol-buffers/docs/proto#on... (Insert joke here about Google engineers just copying around protobufs.)