[boost] Cxx dual library

Subject: [boost] Cxx dual library
From: Edward Diener (eldiener_at_[hidden])
Date: 2016-06-02 14:55:27

I have finished all the main work on the Cxx dual library at 
https://github.com/eldiener/cxx_dual. The library is also in the Boost 
Library Incubator at
http://rrsd.com/blincubator.com/bi_library/cxx_dual-2/?gform_post_id=1597.

The Cxx dual library, or CXXD for short, is a C++ macro header-only 
library which chooses between using a Boost library or its C++ standard 
equivalent library for a number of different C++ implementations, while 
using the same code to program either choice. An 'implementation' is a 
Boost library which has a C++ standard library equivalent whose public 
interfaces are nearly the same in both cases. An 'implementation' is 
called a 'dual library' in this documentation, or 'CXXD-mod' for short.

The library does this by defining object-like macros for including the 
appropriate header file and namespace or using either the Boost library 
version or the C++ standard library version of a particular dual 
library. CXXD currently supports twenty eight different dual libraries, 
where the Boost version and the C++ standard version is nearly 
interchangeable in some respects. CXXD also provides a macro-based 
solution for distinguishing between the Boost version and the C++ 
standard version of a dual library so that specific code for a 
particular dual library choice may be written in those cases where the 
public interfaces diverge.

The library came out of my initial PR to add such a feature to 
Boost.Config, and then I decided to create a separate library and expand 
on the functionality. The gist of the library is to write a single set 
of code for a particular implementation and have it work whether or not 
that code targets a Boost implementation or its C++ standard equivalent. 
The default algorithm will choose the C++ standard implementation if it 
is available, otherwise it chooses the Boost implementation. The default 
can be overriden for any of the 28 different implementations which CXXD 
supports.

With all the talk about supporting C++11 or C++14 in new code, the 
library offers a way of supporting C++11 or C++14 standard libraries if 
available whether one writes in C++03 dialect or uses the new language 
features of C++11 on up. The Cxx dual library itself, being macro based, 
should work with any C++ code at that code's language level. The library 
itself is NOT, repeat NOT, an attempt to enforce a C++ language level 
for anybody who wants to use it.

I have a little more work I am doing on increasing the support for Boost 
Build in the library, but all the central implementation of the library 
is complete in my mind.

Questions, comments, or bug reports are always welcome, either here in 
this mailing list, in the Boost Library Incubator, or as Github issues, 
by those who are interested in trying the library out or reading the 
documentation.

I will be using CXXD in another library on which I am working but 
hopefully others will find a use for it in their own code.