Re: Run-time creation of an object of a dynamically determined class
Kodi Arfer <withheld@domain.tld> wrote:
Suppose I've got a base-class pointer which is pointing to an object
that belongs to any of a number of derived classes. (Please excuse my
brace style from Saturn.)
struct Barney
{Barney() {};
virtual void greeting() {cout << "Barney says hello.\n";};};
struct Dave : public Barney
{Dave() {};
virtual void greeting() {cout << "Dave says hello.\n";};};
struct Dan : public Barney
{Dan() {};
virtual void greeting() {cout << "Dan says hello.\n";};};
void funkshun()
{Barney *bp1 = &ADaveOrADan;
Barney *bp2;
...}
Now, suppose I want to make bp2 point to a new, dynamically allocated
object; not just any object, but one of the same class as *bp1.
The simplest solution is a virtual 'factory' function in the base class
that must be defined in each Derived class to the actual creation
its a one liner but needs definition, such as [not tested]:
struct Barney
{
virtual void greeting();
virtual Barney *create()=0; // pure virtual function
virtual ~Barney(){} // virt. dtor so Derived dtor is used to
// destruct Barney *'s.
};
template <class Derived>
struct BarneyCreate:public Barney
{
Barney *create() { return new Derived;}
};
struct Dave:public BarneyCreate<Dave>
{
void greeting();
};
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