[boost] C++03 and C++11 ABI compatibility for compiled libraries

Subject: [boost] C++03 and C++11 ABI compatibility for compiled libraries
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-05-13 08:08:31

Hi,

I would like to raise the issue of binary compatibility of compiled Boost
libraries between C++03 and C++11. I faced this problem with gcc on Linux,
but other compilers and platforms may be affected as well.

To summarize the problem:

* Most, if not all Linux distributions build packages in C++03 mode. This
is also the default in gcc.
* Some Boost libraries conditionally use C++11 features in their binary
interfaces (see [1] as an example). This makes C++03 and C++11 versions of
the library binary incompatible.
* Given that, users are unable to use C++11 in their code that uses Boost
because of linker failures.

I don't have the complete list of the offending C++11 features that break
ABI, but it would seem that at least scoped enums and rvalue references are
among them. Are there any more?

I would like to hear opinions on the possible course of action to tackle
this problem. Currently, I see 2 choices:

1. Avoid using C++11 features in binary interfaces. This may also mean
avoiding STL types in binary interfaces, if they differ between C++03 and
C++11 (I didn't verify that). This is my suggested hotfix solution for
Boost.Filesystem [1] and the approach I took in Boost.Log. Obviously, this
cripples code and error prone, but it keeps a single binary that can be
used from any flavor of C++ on the user's side.
2. Compile different versions of Boost libraries, for each supported C++
version. The C++ version should be encoded into the library file names, so
that different versions can coexist. This would require changes in
Boost.Build and autolinking support code, but I think this would be a
better long-term solution.

Opinions?

[1] https://svn.boost.org/trac/boost/ticket/6779