Re: SFINAE and non member functions detection.
On 2010-12-09 01:15, Daniel Kr?gler wrote:
On 12/8/2010 12:56, german diago wrote:
It would have been a good idea, if you would have resolved the used
entities like the Type template for us. Without this information there
are several reasons of failure. It is also not clear to me, what the
exact aim of the trait is. Do you want that the trait returns
true in the following situation:
DEFINE_HAS_FREE_FUNCTION_TRAIT(bar);
void bar(double);
static_assert(HasFreeFunctionbar<int>::value, "Ouch"); // OK?
It would return true, because int is convertible to double. I believe
that your originally intended approach would behave similarly. But is
that intended?
If you are searching for an ADL-based function search you will observe that
correspondingly named functions with fundamental types as argument
need to be declared *before* the trait definition.
Here is one possible approach to solve the problem you seem to intend to
solve (quick & dirty, not something to be proud of):
The following is somewhat less intrusive: All internals have been moved into
"non-public" namespaces. I also replaced your deduction mechanism by a different
approach. Assuming the three used C++0x components are replaced by corresponding
C++03 versions, this should work well with e.g. the Comeau compiler.
#include <type_traits>
#include <utility>
namespace details {
struct never{};
}
#define DEFINE_HAS_FREE_FUNCTION_TRAIT(name) \
namespace details_##name {\
details::never name(...);\
}\
namespace details {\
using namespace details_##name;\
\
template<class T>\
struct has_free_function_##name##_impl {\
typedef std::integral_constant<bool,\
!std::is_same<decltype(name(std::declval<T>())),\
details::never>::value> result;\
};\
}\
template<class T>\
struct has_free_function_##name :\
details::has_free_function_##name##_impl<T>::result {}
HTH & Greetings from Bremen,
Daniel Kr?gler
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