Size-wise, the only difference between your "Lite" structure and the current
protobuf classes is that it wouldn't have a virtual table pointer or a
cached byte size. Do these really make that much difference?
On Wed, Dec 17, 2008 at 9:11 PM, Shaun Cox <shaun8...@gmail.com> wrote:
>
> As stated by previous posts (the uint16 one in particular), protobuf C+
> + is not designed for extremely-memory-constrained systems. I was
> curious about the decision to not make the "bare bones" structure of
> the message public and provide a way to construct one from another.
> For example right now the generated code looks something like this:
> couch.proto:
> message Couch
> {
> required uint32 width;
> required uint32 length;
> }
>
> couch.pb.h:
> class Couch : public ::google::protobuf::Message {
> public:
> Couch();
> // rest of public interface...
> private:
> // pb data members
> uint32 width_;
> uint32 length_;
> // more pb data member
> };
>
> If pb provided a "bare bones" structure it might look something like:
> couch.pb.h:
> class Couch : public ::google::protobuf::Message {
> public:
> struct Lite {
> Lite(const Couch& from);
> uint32 width_;
> uint32 length_;
> };
> Couch();
> Couch(const Couch::Lite& from);
> // rest of public interface...
> private:
> // pb data members
> Lite impl_;
> // more pb data member
> };
>
> First off, the API for constructing one from another is more just to
> show an example than anything else. Exposing the underlying structure
> allows you to store smaller in-memory copies of the message. This
> comes into play more when the structure is part of a larger class that
> isn't going across the wire.
>
> class LivingRoom {
> Couch::Lite couches[10];
> };
> class Apartment{
> LivingRoom rooms[3];
> };
> class Complex {
> Apartment apartments[10000];
> };
> class City {
> Complex complexes[100000];
> }
>
> It seems wasteful to have Couch when you could just as well have
> Couch::Lite. With a change like this, if you aren't as concerned with
> memory usage, there is no change to how pb behaves or how you use
> it.
>
> Shaun
> >
>
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