There are 14998 palindromic numbers in [1, 50000000).

I want to define a function that finds them out at compile-time, populates an std::array<int, 14998> and returns it.

I have an idea but cannot compile it. What am I doing wrong ?

#include <array>

bool is_valid(int src)noexcept {
    auto ret{ 0 }, cpy{ src };
    do {
        ret = ret * 10 + src % 10;
    } while ((src /= 10) != 0);
    return ret == cpy;
}

std::array<int, 14998> constexpr build()noexcept {
    std::array<int, 14998> ret{};
    for (auto i{ 1 }, j{ -1 }; i != 50000000; ++i) {
        if (is_valid(i)) {
            ret[++j] = i;
        }
    }
    return ret;
}

int main() {
    auto constexpr lut{ build() };
    return 0;
}