C++11 creating static array from a parameter pack

Question

Is it possible to create a static const array with values from template parameter pack? I tried the following code, but gcc 4.8.1 gives "error: parameter packs not expanded"

template<int... N>
struct ARRAY_OF_DIMS
{
    static constexpr size_t NDIM = sizeof...(N);
    static const int DIMS[NDIM];
};

template<int... N>
const int ARRAY_OF_DIMS<N>::DIMS[ARRAY_OF_DIMS<N>::NDIM] = { N... };

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K-ballo K-ballo · Accepted Answer · 2013-06-11T15:52:13

Try with:

template<int... N>
const int ARRAY_OF_DIMS<N...>::DIMS[ARRAY_OF_DIMS<N...>::NDIM] = { N... };

The parameter pack in ARRAY_OF_DIMS<N> is the one that is not being expanded. Every parameter pack that is not an argument to sizeof... has to be expanded.

C++11 creating static array from a parameter pack

1 Answers