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copied!<p>We still lack a lot of helpers to manipulate variadic parameter packs (or I am not aware of them). Until a nice Boost library bring them to us, we can still write our own.</p> <p>For example, if you are willing to postpone your arrays initialization to the constructor body, you can create and use a fonction that copies part of the parameter pack to an output iterator:</p> <pre><code>#include <array> #include <cassert> #include <iostream> // Copy n values from the parameter pack to an output iterator template < typename OutputIterator > void copy_n( size_t n, OutputIterator ) { assert ( n == 0 ); } template < typename OutputIterator, typename T, typename... Args > void copy_n( size_t n, OutputIterator out, const T & value, Args... args ) { if ( n > 0 ) { *out = value; copy_n( n - 1, ++out, args... ); } } // Copy n values from the parameter pack to an output iterator, starting at // the "beginth" element template < typename OutputIterator > void copy_range( size_t begin, size_t size, OutputIterator out ) { assert( size == 0 ); } template < typename OutputIterator, typename T, typename... Args > void copy_range( size_t begin, size_t size, OutputIterator out, T value, Args... args ) { if ( begin == 0 ) { copy_n( size, out, value, args... ); } else { copy_range( begin - 1, size, out, args... ); } } template < int N > struct DoubleArray { std::array< int, N > p; std::array< int, N > q; template < typename... Args > DoubleArray ( Args... args ) { copy_range( 0, N, p.begin(), args... ); copy_range( N, N, q.begin(), args... ); } }; int main() { DoubleArray<3> mya(1, 2, 3, 4, 5, 6); std::cout << mya.p[0] << mya.p[2] << std::endl; std::cout << mya.q[0] << mya.q[2] << std::endl; } // Ouput: // 13 // 46 </code></pre> <p>As you can see, you can (not so) easily create your own algorithms to manipulate parameter packs; all is needed is a good understanding of recursion and pattern matching (as always when doing Template MetaProgramming...).</p>

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