Peter Dimov wrote:
Peter Dimov wrote:
Ian McCulloch wrote:
Peter Dimov wrote:
[...]
I don't get it: can't you detect whether nested::result<nested(T)>::type exists? As long as the primary template of nested::result is defined as an empty struct this should work fine(?).
No, consider what happens when 'nested' is int (*) (), for example.
Hm, it can't be int (*) (), because result_of will not attempt to look for a nested result, but it can be an user-defined type with no nested result, or a member named result.
Wouldn't both those cases (no nested result, or a member named result) cause a substitution failure? #include <iostream> struct foo { template <typename T> struct result { typedef int type; }; }; struct bar { template <typename T> struct result {}; }; struct baz { void result() {} }; struct bat { }; void func(...) { std::cout << "func(...)\n"; } template <typename T> typename T::result<T(int)>::type func(T const& x) { std::cout << "func(T const&)\n"; return typename T::result<T(int)>::type(); } int main() { func(foo()); func(bar()); func(baz()); func(bat()); } This compiles cleanly with g++ 3.3.4 and produces func(T const&) func(...) func(...) func(...) Cheers, Ian