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Subject: [boost] [RPC] Compile-time reflection for RPC and mocking
From: Peter Bindels (dascandy_at_[hidden])
Date: 2014-12-08 09:27:33

Hi all,

I've searched through the Boost mailing list history to find related emails
and the last I found was from January where Oleg Labutin and Hartmut Kaiser
discussed compile-time reflection in the context of RPC mechanisms.

Based on Hartmut's speech last Saturday introducing HPX and explaining a
bit about async/future/promise I tried to implement a simple RPC mechanism
that uses then to decouple work and the result I have so far is very
promising. I have a simple interface with a call that returns a future, and
the caller does not distinguish between calling the actual object and
calling on a proxy, as both return a future<T>. It does what the discussion
mentions - serialize the name of the interface and function, as well as the
arguments (basically the mangled name of the interface function) to ensure
there are no mismatches.

I would like to take this oppurtunity to propose two things:

- I can work on this idea to work it out into a full RPC mechanism, to be
proposed for Boost.RPC, if there is enough interest. Currently it uses
macros to generate and wrap functions, and a simple serializer that
serializes in the same way that Protobuf and Thrift also serialize.
- Given a compile-time reflection method, the entire proxy class and
dispatch class can be auto-generated from the interface class - the full
code for registering an interface with the RPC mechanism would collapse to
RPC::Register<T>(); To do so, it would need two language additions. It
needs access to a compile-time iterator over functions and traits about the
argument types, return type, name and whether it is a virtual function. For
the prototype this can be manually generated for an interface to show it
works. Additionally, it would need to be able to use such a definition to
instantiate a virtual function from a base class - basically, hooking up an
std::function<X> to a virtual function X directly. I think this is
well-implementable (probably reusing most code from lambdas for the link
code), but I don't know whether that's true.

On the second note, I also proposed a Mock library a few years ago. This
basically fell flat on the code that I suggested being very unsafe and
using many hackish methods to mock functions. Using the compile-time
reflection proposed for the second bullet I would be able to replace the
entire hackishness from that with 100% compliant code, with only one minor
regression in functionality. That should make it Boost-OK at least from a
language standards perspective.

Any ideas? Reactions on RPC or Mocking?

Best regards,
Peter Bindels

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