Hi, I wonder that how to access metadata in runtime. If I pre-compute something and save them into a template ARRAY<int N>, how can I random access the metadatas in runtime? What I can only do is binary searching. Is it possible to do in constant time, or there exist some functions in MPL doing this? #include<cstdio> using namespace std; template<int N> struct ARRAY { static const int a = ARRAY<N - 1>::a * 2; }; template<> struct ARRAY<0> { static const int a = 1; }; template<int LOWER, int UPPER> struct BS { static const int MID = UPPER + LOWER >> 1; typedef BS<MID + 1, UPPER> GREATER; typedef BS<LOWER, MID> LESS; static inline int binary_search(int n) { if(n > MID) return GREATER::binary_search(n); else return LESS::binary_search(n); } }; template<int N> struct BS<N, N> { static const int MID = N; typedef ARRAY<MID> result; static inline int binary_search(int n) { return result::a; } }; int main() { int n; printf("2^n n:"); scanf("%d", &n); printf("ARRAY<%d>::a = %d\n", n, BS<0, 30>::binary_search(n)); main(); return 0; }