generic shared_ptr as member of a class

Question

I want to have a shared_ptr as a member of a class, but the type that the shared_ptr manages is different each time and is only known at run time. Is there any way to declare such a member and init it later?

Answer 1

Yes.

Use runtime polymorphism which means define a common base class, say Base and declare the common interfaces as virtual functions in it, then derive from it and implement the virtual functions in the derived classes. If you do so, then you can use like this:

std::share_ptr<Base> ptr;
//now ptr can store an instance of any derived class from Base

Or you could use boost::any if it is not possible to define a common base class. If you cannot use Boost, then you can define any class yourself. Search for Type Erasure on this site and in google.

The following is a two-pages article on Type Erasure, and you can find an implementation of boost::any on the second page (though not complete):

• What Type Erasure Can Do About It

Answer 2

If the types are unrelated, you can use something like Boost.Any for this. Otherwise, do what @Nawaz says .