Help with Code Validation of Variadic templates

[Larry Evans]

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
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