我的 Design Pattern 之旅 [1]：Strategy Pattern (4) - C++ Function Pointer 實現

Strategy Pattern ISO C++ Function Pointer 實現：最原始的策略替換機制

核心代碼

class Grapher {
public:
    typedef void (*pfDraw)();
    Grapher(pfDraw draw = 0) : _draw(draw) {}
    void drawShape() const { if (_draw) _draw(); }
    void setShape(pfDraw draw) { _draw = draw; }
protected: pfDraw _draw;
};

class Triangle { public: static void draw() { cout << "Draw Triangle" << endl; } };
class Circle { public: static void draw() { cout << "Draw Circle" << endl; } };
class Square { public: static void draw() { cout << "Draw Square" << endl; } };

int main() {
    Grapher grapher(Square::draw); grapher.drawShape();
    grapher.setShape(Circle::draw); grapher.drawShape();
}

執行結果

Draw Square
Draw Circle

本質：介面定義函數簽名 → 函數指標類型定義簽名。所有傳入函數必須符合指標類型。C++ 函數指標啟發 C# Delegate 實現 Strategy。