std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>::extract

#include <cassert>
#include <flat_map>
#include <print>
#include <type_traits>
#include <utility>
#include <vector>

int main()
{
    std::flat_map<int, double> map{{1, 1.1}, {2, 2.2}, {3, 3.3}};
    const auto size{map.size()};
    
    auto c{std::move(map).extract()};
    assert(c.keys.size() == size);
    assert(c.values.size() == size);
    assert(map.empty());
    assert(map.keys().empty());
    assert(map.values().empty());
    
    // The default keys and values containers are std::vector:
    static_assert(std::is_same_v<decltype(c.keys), std::vector<int>>);
    static_assert(std::is_same_v<decltype(c.values), std::vector<double>>);
    
    std::println("keys: {}", c.keys);
    std::println("values: {}", c.values);
}

Вывод:

keys: [1, 2, 3]
values: [1.1, 2.2, 3.3]