我的 Design Pattern 之旅 [1]：Strategy Pattern (7) - C# Generics 實現

Strategy Pattern C# Generics 實現：編譯期類型安全與運行期靈活結合

核心代碼

interface IDrawStrategy { void draw(); }

class Grapher where T : class, IDrawStrategy, new() {
    private T _drawStrategy = default(T);
    public Grapher() { _drawStrategy = new T(); }
    public void drawShape() { if (_drawStrategy != null) _drawStrategy.draw(); }
    public void setShape(T drawStrategy) { _drawStrategy = drawStrategy; }
}

class Triangle : IDrawStrategy { public void draw() { Console.WriteLine("Draw Triangle"); } }
class Circle : IDrawStrategy { public void draw() { Console.WriteLine("Draw Circle"); } }
class Square : IDrawStrategy { public void draw() { Console.WriteLine("Draw Square"); } }

class Program {
    public static void Main() {
        Grapher grapher = new Grapher();
        grapher.drawShape();
        Grapher grapher2 = new Grapher();
        grapher2.drawShape();
    }
}

執行結果

Draw Square
Draw Circle

關鍵差異分析

GoF 原文：Template methods use inheritance to vary part of an algorithm. Strategies use delegation to vary the entire algorithm.

Known Use：Eclipse Plugin 架構，無需修改核心即可擴充功能。