Multiple data types within one vector of pointers using templates - oop

Question

I have two classes seen below,
template <typename T> class node {
public:
int NodeID;//ID used to identify node when inserting/deleting/searching
T data;//generic data encapsulated in each node.
std::vector<node*> children;//child nodes, list of ptrs
std::vector<node*> parents;//parent nodes list of ptrs
};
template<typename T> class DAG {//Class for the graph
std::vector<node<T>*> Nodes;//Vector of node ptrs, this is how we define a DAG;
}
I was wondering whether its possible using templates to have the vector of nodes contain nodes of multiple types? Something like this.
std::vector<node*> Nodes = {node<int>*,node<string>*, ...}

Answer 1

I suggest that you use polymorphism and create a non-template base class:
struct nodebase {
nodebase(int id) : NodeID{id} {}
virtual ~nodebase() = default; // to be able to delete via base class pointer
virtual void print(std::ostream& os) const {
os << NodeID;
}
int NodeID; // ID used to identify node when inserting/deleting/searching
std::vector<std::unique_ptr<nodebase>> children; // child nodes, list of ptrs
std::vector<nodebase*> parents; // parent nodes list of ptrs
};
// to be able to print all nodes, calls the overridden `print` method:
std::ostream& operator<<(std::ostream& os, const nodebase& nb) {
nb.print(os);
return os;
}
With that base class, your node<T> could look like this:
template <typename T>
class node : public nodebase {
public:
// constructor taking `id` + the arguments needed for `T`:
template<class... Args>
node(int id, Args&&... args) : nodebase{id}, data{std::forward<Args>(args)...} {}
void print(std::ostream& os) const override {
nodebase::print(os);
os << ',' << data;
}
T data; // generic data encapsulated in each node.
};
And you could use it like so:
int main() {
std::vector<std::unique_ptr<nodebase>> Nodes;
Nodes.emplace_back(std::make_unique<node<int>>(1, 12356));
Nodes.emplace_back(std::make_unique<node<std::string>>(2, "Hello world"));
for(auto& ptr : Nodes) {
std::cout << *ptr << '\n';
}
}
Output:
1,12356
2,Hello world