minimum instantiate class object, when query getInstance

User of my library will ask for an instance of any class via getInstance<T>().

Among all classes {T1,T2,T3,...,Tn} that user asks (appearance of callling getInstance<T>()) in a certain program, if there is a pair of (i,j) and Ti derived from Tj, I will create only the bigger one, e.g. Ti.

A more complex situation, assume that user's code code ask me to create :-

• Physic
• Rigid
• Constraint

• Graphic

  and their inheritance is as followed:-

My code will create minimum amount of classes that cover the whole tree.
In this case, the best solution are 3 : Rigid, Constraint, Graphic.

If there are many minimum solutions, any one of them are OK.

Here is what I dream :-

template<class T> T* getInstance(){
    //?
}
class B{};
class C{};
class D : public B{};
int main(){
    //..... allow to insert some code here ...... (a little less preferable)
    B* b=getInstance<B>();   //return D*  (implicited cast to B*)
    C* c=getInstance<C>();   //return C*
    D* d=getInstance<D>();   //return D* 
    assert( static_cast<D*>(b) == d );
    delete d;    delete c;
    //no memory leak
}

How to do it?
This is closest question : Create "custom typeid" for many types AND cache their sizeof()

I feel that it is possible : I have to cache the type by using some lambda / std::function , but it is too rough from a concrete idea.

Just in case it is not so obvious - this is not a homework / interview.