解開一個可變參數模板類的模板參數，常量和常量數組

Question

我很新的C++ 2011的可變參數模板，我想知道，如果一招存在做以下的事情：

template<typename T, unsigned int... TDIM> class VariadicTest 
{ 
    public: 
     static const unsigned int order_const = sizeof...(TDIM); 
     static const unsigned int size_const = // TDIM1*TDIM2*TDIM3... 
     static const unsigned int dim_const[order_const] = // {TDIM1, TDIM2, TDIM3...} 
                  // if not possible : 
                  // dim_const[64] = {TDIM1, TDIM2, TDIM3, 0, ..., 0} 

}; 

有沒有什麼「竅門」做這樣的事情？

非常感謝。

Answer 1

這裏是實現兩個其他的功能的方式：

template<unsigned int... T> struct mul; 
template<unsigned int L,unsigned int... T> struct mul<L,T...> 
{ 
static const int val= L*mul<T...>::val; 
}; 
template<unsigned int L> struct mul<L> 
{ 
static const int val= L; 
}; 

template<typename T, unsigned int... TDIM> class VariadicTest 
{ 
    public: 
     static const unsigned int order_const = sizeof...(TDIM); 
     static const unsigned int size_const = mul<TDIM...>::val; 
     static const unsigned int dim_const[order_const]; 
}; 
template<typename T, unsigned int... TDIM> 
const unsigned int VariadicTest<T,TDIM...>::dim_const[order_const] = {TDIM...}; 

測試：http://liveworkspace.org/code/cfb0ec09a05931cfcc00edf29866e716

Answer 2

這裏有一個部分答案，它確實是order_const和size_const。但我看不到如何去做dim_const呢。

#include<iostream> 
using namespace std; 

template<typename T, unsigned int... TDIM> 
class VariadicTest; 

template<typename T> 
class VariadicTest<T> 
{ 
    public: 
     static const unsigned int order_const = sizeof...(TDIM); 

     static const unsigned int size_const = 1; 
}; 
template<typename T, unsigned int baseTDIM, unsigned int... others> 
class VariadicTest<T, baseTDIM, others...> 
{ 
    public: 
     static const unsigned int order_const = sizeof...(TDIM); 
     static const unsigned int size_const = baseTDIM * VariadicTest<T,others...> :: size_const;  
}; 

int main() { 
     VariadicTest<double, 9, 4, 5> x; 
     cout << x.order_const << endl; 
     cout << x.size_const << endl; 
}