std::vector can be used in constexpr context: vectors can be created, modified, and destroyed during constant evaluation. The compiler's constexpr evaluator handles dynamic memory allocation and deallocation within the evaluation, provided no allocation persists to runtime.

Before this, compile-time collections required std::array with a fixed size known in advance, or manual constexpr-compatible data structures. constexpr std::vector allows variable-length computation during constant evaluation using the same container used at runtime.

#include <print>
#include <vector>

consteval int sum_first_n(int n) {
    auto v = std::vector<int>();

    for (auto i = 1; i <= n; ++i) {
        v.push_back(i);
    }

    auto total = 0;

    for (auto x : v) {
        total += x;
    }

    return total;
}

int main() {
    constexpr auto result = sum_first_n(10);

    std::println("sum of 1..10 = {}", result);
}