C++Templates第16章テンプレートと継承例

#include <iostream>

using namespace std;

//     
template <typename Base, int D>
class Discrim : public Base
{
public:
  Discrim() {
    cout<<"Discrim()"<<endl;
  }
  
};

//  Discrim    PolicySelector             
template <typename set1, typename set2, typename set3, typename set4>
class PolicySelector : public Discrim<set1, 1>, public Discrim<set2, 2>, public Discrim<set3, 3>, public Discrim<set4, 4>
{
};

class DefaultPol1 {
public:
  void print() {
    cout<<"p1 print()"<<endl;
  }
};

class DefaultPol2 {
public:
  void print() {
    cout<<"p2 print()"<<endl;
  }
};

class DefaultPol3 {
public:
  void print() {
    cout<<"p3 print()"<<endl;
  }
};

class DefaultPol4 {
public:
  void print() {
    cout<<"p4 print()"<<endl;
  }
};

//           
class DefaultPols
{
public:
  typedef DefaultPol1 dp1;
  typedef DefaultPol2 dp2;
  typedef DefaultPol3 dp3;
  typedef DefaultPol4 dp4;
};

class DefaultPolArgs : virtual public DefaultPols {};

//           policy  
// 1
template <typename Policy>
class Policy1_is : virtual public DefaultPols
{
public:
  typedef Policy dp1;
  
  virtual void print() {
    dp1 dd;
    dd.print();
  }
};

// 2
template <typename Policy>
class Policy2_is : virtual public DefaultPols
{
public:
  typedef Policy dp2;
  
  virtual void print() {
    dp1 dd;
    dd.print();
  }
};

// 3
template <typename Policy>
class Policy3_is : virtual public DefaultPols
{
public:
  typedef Policy dp3;
  
  Policy3_is() {
    cout<<"Policy3_is()"<<endl;
  }
  
  virtual void print() {
    dp1 dd;
    dd.print();
  }
};

// 4
template <typename Policy>
class Policy4_is : virtual public DefaultPols
{
public:
  typedef Policy dp4;
  
  virtual void print() {
    dp1 dd;
    dd.print();
  }
};

//           
template <typename PolicySet1 = DefaultPolArgs,
	  typename PolicySet2 = DefaultPolArgs,
	  typename PolicySet3 = DefaultPolArgs,
	  typename PolicySet4 = DefaultPolArgs>
class BreadSlicer
{
public:
  //      ，PolicySelector                    
  //        PolicySelector    ，               。。。
  //             ？？
  typedef PolicySelector<PolicySet1, PolicySet2, PolicySet3, PolicySet4> policies;
  
  void print() {
    typename policies::dp1 p1;
    p1.print();

    typename policies::dp2 p2;
    p2.print();
    
    typename policies::dp3 p3;
    p3.print();
    
    typename policies::dp4 p4;
    p4.print();
  }
  
};

class CustomPoliA
{
public:
  void print() {
    cout<<"CustomPoliA print()"<<endl;
  }
  
};

class CustomPoliB
{
public:
  void print() {
    cout<<"CustomPoliB print()"<<endl;
  }
  
};

int main(int argc, char **argv) 
{    
    BreadSlicer<Policy3_is<CustomPoliA>, Policy4_is<CustomPoliB> > bc;
    bc.print();
    
    return 0;
}


Starting: /home/robertkun/projects/tevent/build/tevent
p1 print()
p2 print()
CustomPoliA print()
CustomPoliB print()
*** Exited normally ***