On Mon, Oct 6, 2008 at 6:58 AM, Mathias Gaunard <mathias.gaunard@ens-lyon.org> wrote:
Daniel Walker wrote:
That's great news! That would do the trick!
Indeed, it's pretty cool. In C++0x, if you write
template<typename T> auto foo(T&& t) -> decltype(t.foo()) { return t.foo(); }
Then that definition is only visible if T has a nullary foo member function. It's basically the same as type inference in functional programming.
As of today, in GCC 4.4, you can do something equivalent but have to be significantly more verbose:
So, I tried your suggestion with gcc 4.4, but I got an error. #include <cstddef> template<typename T, size_t Cond> struct foo_type { typedef decltype(((T*)0)->foo()) type; }; template<typename T> typename foo_type<T, sizeof(((T*)0)->foo() > 0)>::type foo(T&& t) { return t.foo(); } struct t0 { int foo() { return 0; } }; int main() { t0 x; foo(x); // error: no matching function for call to 'foo(t0&)' } If I take away the && in foo(), I get ICE. Any idea what's wrong here? Daniel