Mathias Gaunard writes:
Christian Holmquist wrote :
I think the doc_file_descriptor example should show how to create an object directly in the vector<file_descriptor> using emplace functions, as boost::move can't detect true rvalues as in c+0x.
boost::interprocess::vector<file_descriptor> v; v.push_back(file_descriptor("filename")); // <- Fails
Why does it fail? I thought rvalues were properly detected.
Correction: If you have these overloads: push_back(const T &x); push_back(BOOST_RV_REF(T) x); Then 1 is chosen because derived to base conversion is stronger than the conversion operator. But if you disable const overload with enable_if<is_movable<T> > then you can do this: v.push_back(file_descriptor("filename")); but this will also work (and seems dangerous): file_descriptor f; v.push_back(f); //Note, no "move" In Interprocess containers I've chosen a more verbose and limited approach: //Catch by value works file_descriptor temp(get_file_descriptor()); //Now explicit move v.push_back(boost::move(temp)); You can also use a catch by value approach with this library: push_back(movable m); that will work with both: v.push_back(boost::move(temp)); v.push_back(movable()); The downside is that you always create a temporary and code will not conform to C++0x. As you mentioned, limitations of the library are not mentioned in the documentation and that's a big hole. A little example to play a bit: #include <boost/move_semantics/move.hpp> #include "movable.hpp" //Catch by value void function(movable m) {} //Catch by reference void function_ref(const movable &m) {} //Catch by reference void function_ref(BOOST_RV_REF(movable) m) {} int main() { movable m; movable cm; //move returns rv ref BOOST_RV_REF(movable) r = boost::move(m); //Conversion operator applied BOOST_RV_REF(movable) q = movable(); //Dangerous for a container if const overload is disabled BOOST_RV_REF(movable) s = m; //Catch by value, ok m = movable(); //Does not compile //function(m); //Compiles function(movable()); //Does not compile in C++03 //function_ref(movable()); //Compiles function_ref(boost::move(m)); return 0; } Regards, Ion