Question

Have a interface

class abc {  public: virtual int foo() = 0;   ...  }  class concrete1: public abc {   public: int foo() {   .. }   class concrete2 : public abc {  public: int foo() {  .. }   } 

Now in my main program I need to construct classes based upon a value of a variable

abc *a; if (var == 1)    a = new concrete1(); else    a = new concrete2(); 

Obviously I don’t want these two lines everywhere in the program (please note I have simplified here so that things are clear). What design pattern should I be using if there are any?

Answer 1

You are looking for http://en.wikipedia.org/wiki/Factory_method_pattern