on Thu Jul 05 2007, Lewis Hyatt <lhyatt-AT-princeton.edu> wrote:
cerr << "TEST 2: RVALUE" << endl; { cerr << "\tstarting foreach" << endl; BOOST_FOREACH(int const& i, get_vec(5)); } ... If I compile it with the RVO enabled, I get the following output: ------------- TEST 1: LVALUE container was constructed starting foreach container was destructed
TEST2: LVALUE, REFERENCE container was constructed starting foreach container was destructed TEST 2: RVALUE starting foreach container was constructed container was copied container was destructed container was destructed -------------
So in either case, using BOOST_FOREACH requires one extra copy. nt to
I'm not so sure. If you want to avoid seeing the copy that happens when get_vec returns, just do BOOST_FOREACH(int const& i, noisy_vector(5,0)); That's as good an rvalue as any-----^^^^^^^^^^^^^^^^^ and might clarify things for you a bit.
isn't it possible just to bind the temporary to a const reference instead?
That's up to the implementation. At least according to C++98, it's allowed to make a copy when you do that :( -- Dave Abrahams Boost Consulting http://www.boost-consulting.com The Astoria Seminar ==> http://www.astoriaseminar.com