On 3/30/07, Guillaume Melquiond <guillaume.melquiond@ens-lyon.fr> wrote:
Quoting Daniel Walker:
Is this a substitution failure?
There is no substitution in your code, so a substitution failure cannot happen. Here is a real substitution, that does fail properly:
template<class T> struct foo { template<class U> struct bar; };
template<class T, class U> void f(T,U) {}
template<class T, class U> void f(T, typename foo<T>::template bar<T,U>) {}
int main() { f(0,0); }
OK, thanks for the help. I was trying to simplify my code to replicate the error I'm getting, and I may have gone to far. Can you tell me if the following contains a substitution? struct foo { template<class U> struct bar; }; template<class T, class U, class V> struct baz { template<class W> static int f(W*, ...) {} template<class W> static int f(W*, typename W::template bar<U,V>*) {} static const int size = sizeof(f<T>(0, 0)); // error: wrong number of template arguments (2, should be // 1) provided for `template<class U> struct foo::bar' }; int main() { baz<foo, int, int>::size; } This is closer to the has_xxx implementation. Any suggestions would be greatly appreciated!
I am not sure if it will help you though, as I don't know if you can afford to protect the class you want to test (bar) into a dummy template (foo), so that a substitution happens. No template typedef...
Best regards,
Guillaume
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