The rationale for the design of the CXXD library is to provide the least intrusive way of allowing a programmer, using the same code, to use either a Boost library or its C++ standard equivalent library based on whether the C++ standard library is available or not.

Other implementations along these lines involved a great deal of intrusiveness and preprocessing of outside code, and I did not want to follow along those lines no matter how workable such solutions might seem to others. My goal was to make this ability to program either side of dual libraries with the least amount of effort a reality.

While I realized that other programmers might be put off by the use of C++ macros in designing such a library my experience with macro programming and the use of macros told me that the weaknesses of a macro solution were a good compromise with the effectiveness of such a solution in actual usage.

The original design, what was version 1 of the library, was completely macro-based. This version garnered much criticism because of its extensive use of macros in user code and the general dislike of macro use for many programmers.

I subsequently came up with version 2 of the library, which offered both a macro-based way of programming using CXXD and a namespace alias way of programming using CXXD.

Thinking about the dual nature of programming using the library, whether it be macro-based or alias-based, along with all the examples in the doc using both these modes, I realized that these modes are probably just confusing potential users of he library. Therefore, with the latest version 3 of the library I have rearranged the header files and the documentation to provide the basic mode of programming the library, based on a header file that automatically includes what is needed for a dual library and a namespace alias that provides access to the constructs of a dual library. In this mode CXXD macros rarely appear in user code, which should satisfy objections to the library being used by programmers who dislike the use of macros. A low-level macro-based interface still exists for programmers who might want to use its facilities.