///a c++ std::map
public struct std_map(K, V) {
    private map_node!(K, V)* head;
    public size_t size;

    public alias values this;
    public @property V[K] values() {
        if (!head)
            return null;
        V[K] result;
        walkTree(result, head);
        return result;
    }

    private void walkTree(ref V[K] result, map_node!(K, V)* node) {
        if (node.isNull)
            walkTree(result, node.parent);
        else
            result[node.pair.t1] = node.pair.t2;

        if (!node.left.isNull)
            walkTree(result, node.left);

        if (!node.right.isNull)
            walkTree(result, node.right);
    }
}

private struct map_node(K, V) {
    map_node* left;
    map_node* parent;
    map_node* right;
    ubyte isBlack;
    ubyte isNull;
    std_pair!(K,V) pair;
}

private struct std_pair(T1, T2) {
    T1 t1;
    T2 t2;
}