Daniel James wrote:
Try it. std::swap can't swap arrays, boost::swap can. boost::swap will also call swap via. ADL when appropriate and supports compilers that don't support ADL. Which is why it's recommended that 'boost::swap' is used.
Thanks, Daniel. In fact, proper performance of boost::swap /does/ depend on compilers having implemented ADL. But we've found out that for some compilers (including MSVC 7.1, Borland 5.9.3, and Intel 8.1), ADL only works fine when a using-directive ("using namespace std") is used, instead of a using-declaration ("using std::swap"). Luckily this using-directive is hidden within an internal helper function of boost::swap. Peter Simons wrote:
$ cat >test.cpp <<EOF #include <string> #include <boost/swap.hpp>
int main(int, char * []) { std::string a1[42]; std::string a2[42];
boost::swap(a1, a2); // Okay.
using boost::swap; swap(a1, a2); // Does not compile!
return 0; } EOF $ g++ -pedantic test.cpp && ./a.out && echo okay okay
Interesting! Can you tell us whether it picks std::swap or boost::swap? BTW, support for built-in arrays is added to std::swap very recently; it's in the Working Draft. Basically it's my very first (very) little contribution to the Standard :-) 25.4.3 Swap [alg.swap] (www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2914.pdf) says: template<ValueType T, size_t N> requires Swappable<T> void swap(T (&a)[N], T (&b)[N]); 2 Effects: swap_ranges(a, a + N, b) I wonder if GCC has already implemented this new feature. -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center