On 09/24/2012 08:15 PM, Eric Niebler wrote:
I confess to not understanding how the config tests work. When I run "bjam toolset=gcc-4.4 config_test" in libs/config/tests, the tests pass whether or not S_NO_SFINAE_EXPR is defined for gcc-4.4. I'm clearly doing something wrong.
Looks like the test is not good enough then. (I was the one who wrote that particular test, but I don't quite understand the Boost.Config testing mechanism either)
Anyway, here is a test for sfinae-expr that fails with gcc-4.4:
template<typename T> T declval();
struct not_incrementable {};
struct inc { template<typename T> auto operator()(T t) const -> decltype(t++) { return t++; } };
template<typename T> struct wrap {};
template<typename A> int try_inc(wrap<decltype(declval<inc>()(declval<A>()))> *) { return 0; }
template<typename A> not_incrementable try_inc(...) { return not_incrementable(); }
struct X {};
int main() { int x = try_inc<int>(0); // OK not_incrementable y = try_inc<X>(0); // OK, not_incrementable }
SFINAE for expressions also works in C++03, so it would be better if you could have a C++03 testcase.