Question

我试图使用使用SFINAE进行递归的递归静态成员函数从模板结构中的包中剥离参数。我知道我可以使用结构的部分专业化，但是我想尝试这种方式。这是测试代码

#include<type_traits>

template< int NDIM, typename INDEX, typename... REMAINING_INDICES >
struct helper
{
  template< int DIM=0 >
  inline static typename std::enable_if< DIM!=(NDIM-1), int>::type
  f( int const * const strides,
     INDEX index,
     REMAINING_INDICES... indices )
  {
    return index*strides[0]
         + helper<NDIM, REMAINING_INDICES...>::f<DIM+1>( strides+1, indices... );
  }

  template< int DIM=0 >
  inline static typename std::enable_if< DIM==(NDIM-1), int>::type
  f( int const * const strides,
     INDEX index )
  {
    return index;
  }
};

int main()
{

}

gcc8给出：

g++ -std=c++14 main.cpp 
main.cpp: In static member function 'static typename std::enable_if<(DIM != (NDIM - 1)), int>::type helper<NDIM, INDEX, REMAINING_INDICES>::f(const int*, INDEX, REMAINING_INDICES ...)':
main.cpp:41:80: error: expected binary operator before ')' token
          + helper<NDIM, REMAINING_INDICES...>::f<DIM+1>( strides+1, indices... );
                                                                                ^

clang6给出：

clang++ -std=c++14 main.cpp 
main.cpp:41:76: error: expected ')'
         + helper<NDIM, REMAINING_INDICES...>::f<DIM+1>( strides+1, indices... );
                                                                           ^
main.cpp:41:56: note: to match this '('
         + helper<NDIM, REMAINING_INDICES...>::f<DIM+1>( strides+1, indices... );
                                                       ^
main.cpp:40:12: error: expression contains unexpanded parameter pack 'indices'
    return index*strides[0]
           ^
2 errors generated.

有人知道为什么这行不通吗？

带参数包和SFINAE函数的模板化结构

0 个答案: