| // Copyright 2007 Google Inc. All rights reserved. |
| // Author: kenton@google.com (Kenton Varda) |
| // |
| // This is proto2's version of MessageSet. See net/proto/message_set.h to |
| // learn what MessageSets are and how they are used. |
| // |
| // In proto2, we implement MessageSet in terms of extensions, except with a |
| // special wire format for backwards-compatibily. To define a message that |
| // goes in a MessageSet in proto2, you must declare within that message's |
| // scope an extension of MessageSet named "message_set_extension" and with |
| // the field number matching the type ID. So, for example, this proto1 code: |
| // message Foo { |
| // enum TypeId { MESSAGE_TYPE_ID = 1234; } |
| // } |
| // becomes this proto2 code: |
| // message Foo { |
| // extend proto2.bridge.MessageSet { |
| // optional Foo message_set_extension = 1234; |
| // } |
| // } |
| // |
| // Now you can use the usual proto2 extensions accessors to access this |
| // message. For example, the proto1 code: |
| // MessageSet mset; |
| // Foo* foo = mset.get_mutable<Foo>(); |
| // becomes this proto2 code: |
| // proto2::bridge::MessageSet mset; |
| // Foo* foo = mset.MutableExtension(Foo::message_set_extension); |
| // |
| // Of course, new code that doesn't have backwards-compatibility requirements |
| // should just use extensions themselves and not worry about MessageSet. |
| |
| syntax = "proto2"; |
| |
| option optimize_for = LITE_RUNTIME; |
| |
| package proto2.bridge; |
| |
| option java_outer_classname = "MessageSetProtos"; |
| option java_multiple_files = true; |
| |
| message MessageSet { |
| option message_set_wire_format = true; |
| extensions 4 to max; |
| } |