I propose the introduction of BOOST_SYMBOL_IMPORT_VISIBLE to Boost.Config that behaves like BOOST_SYMBOL_IMPORT in all cases except gcc (and like compilers?) where it expands to "__attribute__((visibility("default")))". I believe this is need to address the following two scenarios:
(For gcc, assume all libraries are built with the following ption: -fvisibility=hidden)
********** Scenario 1 ********** Export class MyException from Library A. Catch MyException in Library B, and be able to throw or rethrow it from Library B. Catch MyException in Library C.
I think this is a real problem, but the solution is rather cumbersome - a Boost library header would then have to support: 1) Exporting from dll. 2) Importing to executable. 3) Importing to dll and re-exporting. 4) None of the above (static lib). Looking at http://gcc.gnu.org/wiki/Visibility they suggest that 2 & 3 are the same, and both are __attribute__ ((visibility("default"))) on gcc. Sp my suggestion is that we fix the existing macros to do the right thing and change GCC's BOOST_SYMBOL_IMPORT to __attribute__ ((visibility("default"))). Thoughts? Thanks for raising this, John.