On 08/16/09 09:32, Larry Evans wrote:
On 12/07/07 15:12, Rene Buergel wrote:
I'm currently playing around using mainline with the variadic template
feature and would like to hear some comments on code gcc is rejecting.
#1:
=====
1 template<typename T, T a, T... Args> T max()
2 {
3 return a > max<T, Args>() ? a : max<T, Args>();
4 };
5
6 template<typename T, T a, T b>T max()
7 {
8 return a > b ? a : b;
9 };
int main()
{
unsigned int a = max<unsigned int, 3, 2>();
unsigned int a = max<unsigned int, 3, 2, 5>();
}
=====
Using the non-variadic template, everything works fine. With the
variadic templates, gcc issues an error in line 3:
error: parameter packs not expanded with `...':
note: 'Args'
[snip]
I think this is an instance of bug 40092:
[snip]
OOPS. It's unrealted to bug 40092.
Part of the problem is Args needs to be expanded as follows:
Args...
I think *maybe* the other problem is template function specialization.
Anyway, the workaround is to use template class specializations
as shown in the attached.
HTH.
-Larry
template<typename T, T... Args>struct maxc
;
template<typename T, T Head>struct maxc<T,Head>
{
static T const value=Head;
};
template<typename T, T Head, T... Tail>struct maxc<T,Head,Tail...>
{
private:
static T const tail=maxc<T,Tail...>::value;
public:
static T const value=Head>tail?Head:tail;
};
template<typename T, T... Args> T maxf()
{
return maxc<T,Args...>::value;
}
int main()
{
unsigned int a = maxf<unsigned int, 3, 2>();
unsigned int b = maxf<unsigned int, 3, 2, 5>();
return a==b;
}
