In testing out libraries which use Boost PP, with clang as the compiler, I am seeing a great deal on 'master' of:

..\..\..\boost/archive/detail/basic_serializer.hpp:35:7: error: 'operator=' is a private member of 'boost::noncopyable_::noncopyable' class basic_serializer :

Does anybody know what this is all about ? It is occuring in a number of libraries using serialization.