"is a bad idea".
Using something like Google's Protocol Buffers or a similar system where you generate a standard serialization backend for all the plain old data types you want to send across the network is way less of a pain in the ass.
If you're concerned about the overhead, look at MsgPack or Cap'n Proto - plenty of ways to shave the yak out there without needing to roll your own.
Reflection on the other hand is immensely useful if you want to, for example, automatically generate type-safe bindings for, say, Python or .NET or Java, from your C++ classes.
If I'm not mistaken, he has been working into getting the necessary data available from the compiler directly (which this paper would confirm).
Link to his existing library: http://kifri.fri.uniza.sk/~chochlik/mirror-lib/html/
Absolutely great guy, as well. Really happy to see him still working on this, year over year.
Edit: DYAC.
Games need a lot of iteration, C++ compile times can easily get very long i.e. minutes. You might object that compile times should never be long: "oh this never happens if you do X or Y" but in reality every C++ gamedev shop I've worked at has had long compiles times. Templates and other things of that nature tend to bloat it.
Anyway so reflection helps with:
- Hot-reloading code
- Tweaking reflected values at runtime
- Exposing functions for scripting languages (without having to write lots of repetitive boiler plate code)
- Saving / Loading
Both concerns are about having the need for boilerplate code (either for bindings or for serialization), which is quite repetitive to write and depends on the input types.
Now the possible solutions are from my perspective:
- Write that code by hand, which is quite tedious and error-prone.
- Use some code generator tooling (like protoc) for it. However that might require you to define your types in an IDL before going to code, which leads to an extra step in the development and build process. In my experience this works really well for big teams (because you also have an extra interface documentation against which all parties can work), but it might not be optimal for small teams and rapid iterations.
- Generate the code automatically from the type definitions in your program. Either during compile-time (which would require good compiler support for extracting the relevant details and using them for code generation) or during runtime by reflection. With reflection you are most likely getting the slowest code. But iteration times should be the fastest (no need to change IDL files, run codegen tools, etc.)