Most standard library containers and container adaptors are now usable in constexpr contexts. This includes std::deque, std::forward_list, std::list, std::map, std::set, std::unordered_map, std::unordered_set, std::queue, std::stack, std::priority_queue, and the flat container adaptors, and container operations including construction, insertion, erasure, and iteration.

Prior to this change, only std::vector, std::array, std::string, and a few other types were usable at compile time. Algorithms requiring associative containers, linked lists, or deques could not be evaluated during compilation. This extension unifies runtime and compile-time C++ by making most container operations available in both contexts.

#include <map>
#include <set>
#include <deque>

constexpr int compute() {
    std::map<int, int> m;
    m[1] = 10;
    m[2] = 20;

    std::set<int> s = {3, 1, 4, 1, 5};

    std::deque<int> d;
    d.push_back(100);
    d.push_front(50);

    return m.at(1) + static_cast<int>(s.size()) + d.front();
}

static_assert(compute() == 10 + 4 + 50);

int main() {}