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Language: C++
Expertise: Advanced

Mar 12, 1999

A constructor may not be declared virtual. The easiest way to simulate virtual construction is by defining a virtual member function that returns a constructed object of its class type:

 
class Browser{
public:
  virtual Browser* construct()  { return new Browser; } //virtual default constructor
  virtual Browser* clone() { return new Browser(*this); } //virtual copy constructor
};

class HTMLEditor: public Browser{
public:
  HTMLEditor * construct() { return new HTMLEditor; }//virtual default constructor
  HTMLEditor * clone() { return new HTMLEditor (*this); } //virtual copy constructor
};

The polymorphic behavior of the member functions clone() and construct() enables you to instantiate a new object of the right type, without having to know the exact type of the source object.

 
void create (Browser& br)
{
  Browser* pbr  = br.construct(); 
  //