strategy.cpp

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//: C10:Strategy.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// The Strategy design pattern.
#include <iostream>
using namespace std;

class NameStrategy {
public:
  virtual void greet() = 0;
};

class SayHi : public NameStrategy {
public:
  void greet() {
    cout << "Hi! How's it going?" << endl;
  }
};

class Ignore : public NameStrategy {
public:
  void greet() {
    cout << "(Pretend I don't see you)" << endl;
  }
};

class Admission : public NameStrategy {
public:
  void greet() {
    cout << "I'm sorry. I forgot your name." << endl;
  }
};

// The "Context" controls the strategy:
class Context {
  NameStrategy& strategy;
public:
  Context(NameStrategy& strat) : strategy(strat) {}
  void greet() { strategy.greet(); }
};

int main() {
  SayHi sayhi;
  Ignore ignore;
  Admission admission;
  Context c1(sayhi), c2(ignore), c3(admission);
  c1.greet();
  c2.greet();
  c3.greet();
} ///:~