9constexpr std::array<T, N1 + N2>
arrayConcat(
const std::array<T, N1>& arr1,
10 const std::array<T, N2>& arr2) {
11 std::array<T, N1 + N2> ret{};
12 std::copy_n(arr1.cbegin(), arr1.size(), ret.begin());
13 std::copy_n(arr2.cbegin(), arr2.size(), ret.begin() + arr1.size());