[haberman]

Hmm, I'm not sure I quite get your strategy. If you want to support back to Protobuf 2.5, then you'll need to use proto2 schemas (https://developers.google.com/protocol-buffers/docs/proto). Proto2 schemas will support extensions forever (even after Protobuf 3.0), so there's no need to avoid extensions.

You are only using proto3 schemas if you start your .proto file with 'syntax = "proto3;"': https://developers.google.com/protocol-buffers/docs/proto3 But if you do this, your .proto file will no longer work with Protobuf <3.0.

We have been working on some optimizations to help the linker strip generated code where possible. I recommend compiling with -ffunction-sections/-fdata-sections if you aren't already, and -gc-sections on your linker invocation.

[jiayq84]

So what we do is to keep syntax=proto2, but allow users to compile with both protobuf 2.x and protobuf 3.x libraries. Minumum need is 2.6.1. We kind of feel that this gives maximum flexibility for people who have already chosen a protobuf library version.

[haberman]

Makes sense! All I'm saying is that there is no need to avoid using extensions if that is your strategy. Extensions will work in all versions of the library you wish to support.