Yes, this seems nice: Foo.Builder builder; builder.setBar(builder.getBar().toBuilder().setA(...).build());
But I guess I'm a little worried about its hidden cost if I use it a lot. If message Bar was very large, then would converting it to a builder, setting one value, and converting it back to a message again incur a large cost? That is, is the time cost of setting one of a builder's sub-message's values proportional to the total size of the sub-message? That would be quite different than the cost of setting one of a builder's values, which is constant. If I know that a message of type Foo contains some Foo-specific information, then I'd want to be able to write code that reads a message of type Foo and gives me back that information. Like in your example, I know that a Foo message has some "a" information and some "b" information. I could write a method GetA(Foo) : int32 ... well, Option<int32> anyway. (It might be null.) Then if I later decided to move the field "a" from Bar to Foo I wouldn't have to change client code of GetA(Foo) at all. It would be just as fast, too, because there really isn't any difference between msg.getBar().getA() and msg.getA (). I can do this right now, which is great. But writing is a different story. Let's say I moved "a" from Bar to Foo. I know that I can write to a builder of type Foo.Builder some "a" information and some "b" information. I could write a method SetA (Foo.Builder, int32) : unit that just invokes the setA method in Foo.Builder. But then, if I decided to move "a" back to Bar, then my implementation of SetA(Foo.Builder, int32) : unit has to change a lot. I might have to convert Foo's bar from a message to a builder, set "a" in it, and rebuild the updated Bar message. That doesn't change the type signature of SetA but it might have a big effect on the cost of calling the method. If builders could contain builders, however, then I'd know for sure that I could change where "a" lives without significantly affecting the performance of methods like SetA! And I do those kinds of changes to my protocol a lot--I'm always rearranging how information relates to each other as my applications evolve. Is it just me? On Dec 16, 11:55 am, Jason Hsueh <[email protected]> wrote: > You should be able to pass a builder to some method, and have the method > modify some value of the builder just fine. > > Modifying a value in a sub-message is a bit more inconvenient, but still > doable. If you have some type Bar in type Foo like: > message Bar { > optional int32 a = 1; > optional int32 b = 2; > > } > > message Foo { > optional Bar bar = 1; > > } > > Foo.Builder builder; > builder.setBar(builder.getBar().toBuilder().setA(...).build()); > > Would that work for you? > > > > On Wed, Dec 16, 2009 at 9:24 AM, Mark <[email protected]> wrote: > > I wish I could pass a builder object to a method and have the method > > modify either a value of the builder or a value of a sub-message in > > the builder! > > > I came across this thread, which described exactly the problem I have. > > The Car/Engine example in the thread is perfectly illustrative of my > > scenario. > > >http://groups.google.com/group/protobuf/browse_thread/thread/16997910... > > > Has anyone else been in this same situation? What have you done to > > ameliorate the problem? > > > -- > > > You received this message because you are subscribed to the Google Groups > > "Protocol Buffers" group. > > To post to this group, send email to [email protected]. > > To unsubscribe from this group, send email to > > [email protected]<protobuf%[email protected] > > om> > > . > > For more options, visit this group at > >http://groups.google.com/group/protobuf?hl=en. -- You received this message because you are subscribed to the Google Groups "Protocol Buffers" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/protobuf?hl=en.
