Applying Abstract Factory Pattern: the Loki Way

This article aims to apply the Abstract Factory pattern in C++ applications using the Singleton and AbstractFactory components implemented in the Loki library.
Sample code goes below:

#include <iostream>#include <memory>#include "AbstractFactory.h"#include "Singleton.h"using namespace std;using namespace Loki;// Abstract products A and Bstruct A { virtual ~A(){} };struct B { virtual ~B(){} };// Concrete products A1 and B1struct A1: public A{    A1() { cout << "A1::ctor" << endl; }};struct B1: public B{    B1() { cout << "B1::ctor" << endl; }};// Concrete products A2 and B2struct A2: public A{    A2() { cout << "A2::ctor" << endl; }};struct B2: public B{    B2() { cout << "B2::ctor" << endl; }}; // Traditional method beginsclass AbstractFactory1 { public:         virtual A* CreateA() = 0;        virtual B* CreateB() = 0;};class ConcreteFactory1 : public AbstractFactory1{public:    virtual A* CreateA() { return new A1(); }    virtual B* CreateB() { return new B1(); }        static ConcreteFactory1& Instance() {        static ConcreteFactory1 instance;        return instance;    }protected:    ConcreteFactory1() {}private:    ConcreteFactory1(const ConcreteFactory1&);    ConcreteFactory1& operator=(const ConcreteFactory1&);};class ConcreteFactory2 : public AbstractFactory1{public:    virtual A* CreateA() { return new A2(); }    virtual B* CreateB() { return new B2(); }        static ConcreteFactory2& Instance() {        static ConcreteFactory2 instance;        return instance;    }protected:    ConcreteFactory2() {}private:    ConcreteFactory2(const ConcreteFactory2&);    ConcreteFactory2& operator=(const ConcreteFactory2&);};// Traditional method ends// Loki method beginstypedef AbstractFactory<TYPELIST_2(A, B)> AF;typedef SingletonHolder<ConcreteFactory<AF, OpNewFactoryUnit, TYPELIST_2(A1, B1)> > SCF1;typedef SingletonHolder<ConcreteFactory<AF, OpNewFactoryUnit, TYPELIST_2(A2, B2)> > SCF2;// Loki method endsvoid main(){    cout << "Traditional method:" << endl;    // Create all concrete products using traditional method    auto_ptr<A> pTA1(ConcreteFactory1::Instance().CreateA());    auto_ptr<B> pTB1(ConcreteFactory1::Instance().CreateB());    A *pTA2 = ConcreteFactory2::Instance().CreateA();    delete pTA2;    B *pTB2 = ConcreteFactory2::Instance().CreateB();    delete pTB2;    cout << "Loki method:" << endl;    // Create all concrete products using Loki method    auto_ptr<A> pLA1(SCF1::Instance().Create<A>());    auto_ptr<B> pLB1(SCF1::Instance().Create<B>());    A *pLA2 = SCF2::Instance().Create<A>();    delete pLA2;    B *pLB2 = SCF2::Instance().Create<B>();    delete pLB2;}