Hello All, I know that my idea is trivial but this thing is missing in Boost. In some cases it is useful to have copy-on-write objects. For example, everybody knows that returning std::string from a function is not very efficient (actually that's why in Qt strings are implemented as copy-on-write ones). Consider following code: copy_on_write< std::string > concatenate( const std::string &first, const std::string &second ) { copy_on_write< std::string > result; result->assign( first ); result->append( second ); return result; } // somewhere else std::cout << *concatenate( "Hello,", " world!" ) << std::endl; Here no string copy occurs. One can invent a lot of different applications of copy-on-write techinque (strings, iterators, memory pages). I have an implementation, now let community decide if this can be a part of Boost. Sincerely yours, Maksym Motornyy.