constexpr std::vector

#include <vector>
#include <algorithm>
#include <numeric>
// C++20 allows constexpr dynamic allocation
constexpr int sum_of_squares(int n) {
    std::vector<int> squares;
    squares.reserve(n);
    
    for (int i = 1; i <= n; ++i) {
        squares.push_back(i * i);
    }
    
    return std::accumulate(squares.begin(), squares.end(), 0);
}
// Compile-time sorting
constexpr auto get_sorted_data() {
    std::vector<int> data = {5, 2, 8, 1, 9, 3};
    std::sort(data.begin(), data.end());
    
    // Must return fixed-size type for constexpr
    std::array<int, 6> result;
    std::copy(data.begin(), data.end(), result.begin());
    return result;
}
int main() {
    // Computed at compile time
    constexpr int result = sum_of_squares(5);  // 1+4+9+16+25 = 55
    static_assert(result == 55);
    
    constexpr auto sorted = get_sorted_data();
    static_assert(sorted[0] == 1);
    static_assert(sorted[5] == 9);
    
    return 0;
}