행위패턴-Strategy

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[Strategy]
의도:
다양한 알고리즘이 존재하면 이들 각각을 하나의 클래스로 캡슐화하여 알고리즘의 대체가 가능
하도록 한다. Strategy패턴을 이용하면 클라이언트와 독립적인 다양한 알고리즘으로 변형할 수
있다. 알고리즘을 바구더라도 클라이언트는 아무런 변경을 할 필요가 없다.

다른 이름:
Policy

참고:
Policy-based design이 Strategy을 이용한 디자인 방법이다.
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/////////////////////////////////////////////////////////////////////////////
//
// A Behavioral part of GoF's Design Patterns
//
// - Strategy
//
/////////////////////////////////////////////////////////////////////////////

#include <windows.h>
#include <tchar.h>

#include <iostream>

/////////////////////////////////////////////////////////////////////////////
//
// Strategy
//
//
/////////////////////////////////////////////////////////////////////////////
class Strategy
{
public:
 virtual ~Strategy() {}
public:
 virtual void AlgorithmInterface(void) = 0;
};

template <typename Strategy>
class Context
{
public:
 void operator() ()
 {
  Strategy_.AlgorithmInterface ();
 }

private:
 Strategy Strategy_;
};

class ContextByRunTime
{
public:
 explicit ContextByRunTime (Strategy *s) :
  Strategy_ (s)
 {
 }

public:
 void operator() ()
 {
  Strategy_->AlgorithmInterface ();
 }

private:
 Strategy *Strategy_;
};

class ConcreteStrategyA : public Strategy
{
public:
 virtual void AlgorithmInterface(void)
 {
  std::cout << "ConcreteStrategyA::AlgorithmInterface()" << std::endl;
 }
};

class ConcreteStrategyB : public Strategy
{
public:
 virtual void AlgorithmInterface(void)
 {
  std::cout << "ConcreteStrategyB::AlgorithmInterface()" << std::endl;
 }
};

class ConcreteStrategyC : public Strategy
{
public:
 virtual void AlgorithmInterface(void)
 {
  std::cout << "ConcreteStrategyC::AlgorithmInterface()" << std::endl;
 }
};

/////////////////////////////////////////////////////////////////////////////
//
// Startup
//
//
/////////////////////////////////////////////////////////////////////////////
int _tmain(int argc, _TCHAR* argv[])
{
 ConcreteStrategyA s1;
 ConcreteStrategyB s2;
 ConcreteStrategyC s3;

 ContextByRunTime cr1(&s1);
 ContextByRunTime cr2(&s2);
 ContextByRunTime cr3(&s3);

 Context<ConcreteStrategyA> cc1;
 Context<ConcreteStrategyB> cc2;
 Context<ConcreteStrategyC> cc3;

 std::cout << "by run-time" << std::endl;
 cr1();
 cr2();
 cr3();

 std::cout << std::endl;

 std::cout << "by compile-time" << std::endl;
 cc1();
 cc2();
 cc3();

 return 0;
}
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by run-time
ConcreteStrategyA::AlgorithmInterface()
ConcreteStrategyB::AlgorithmInterface()
ConcreteStrategyC::AlgorithmInterface()

by compile-time
ConcreteStrategyA::AlgorithmInterface()
ConcreteStrategyB::AlgorithmInterface()
ConcreteStrategyC::AlgorithmInterface()