How can I wrap BOOST in a separate namespace?

Question

I'm looking to have two versions of BOOST compiled into a project at the same time. Ideally they should be usable along these lines:

boost_1_36_0::boost::shared_ptr<SomeClass> someClass = new SomeClass();
boost_1_35_0::boost::regex expression("[0-9]", boost_1_35_0::boost::regex_constants::basic);

Answer 1

You'll have a world of trouble linking because the mangled names will be different. And yes, I see you knew that, but it seems like it will be trouble all around.

Answer 2

@Josh: While I agree with the shivering, I still believe this is the better course of action. Otherwise, linking troubles are a certainty. I've had the situation before where I had to hack the compiled libraries using objcopy to avoid definition conflicts. It was a nightmare for platform interoperability reasons because the name mangling works very differently even in different versions of the same compilers (in my case, GCC).

Answer 3

I read (well scanned) through the development list discussion. There's no easy solution. To sum up:

1. Wrapping header files in a namespace declaration

   namespace boost_1_36_0 {
       #include <boost_1_36_0/boost/regex.hpp>
   }
   namespace boost_1_35_0 {
       #include <boost_1_35_0/boost/shared_ptr.hpp>
   }
   

   • Requires modifying source files
   • Doesn't allow for both versions to be included in the same translation unit, due to the fact that macros do not respect namespaces.

2. Defining boost before including headers

   #define boost boost_1_36_0
       #include <boost_1_36_0/boost/regex.hpp>
   #undef boost
   #define boost boost_1_35_0
       #include <boost_1_35_0/boost/shared_ptr.hpp>
   #undef boost
   

   • Source files can simply be compiled with -Dboost=boost_1_36_0
   • Still doesn't address macro conflicts in a single translation unit.

   • Some internal header file inclusions may be messed up, since this sort of thing does happen.

     #if defined(SOME_CONDITION)
     #  define HEADER <boost/some/header.hpp>
     #else
     #  define HEADER <boost/some/other/header.hpp>
     #endif
     

     But it may be easy enough to work around those cases.

3. Modifying the entire boost library to replace namespace boost {..} with namespace boost_1_36_0 {...} and then providing a namespace alias. Replace all BOOST_XYZ macros and their uses with BOOST_1_36_0_XYZ macros.
   • This would likely work if you were willing to put into the effort.