using System;

namespace Wrox.ProCSharp.Generics
{
  public class Shape
  {
    public double Width { get; set; }
    public double Height { get; set; }

    public override string ToString()
    {
      return String.Format("Width: {0}, Height: {1}", Width, Height);
    }
  }
}

namespace Wrox.ProCSharp.Generics
{
  public
 
 class Rectangle : Shape
  {
  }
}

namespace Wrox.ProCSharp.Generics
{
  // contra-variant
  //泛型介面的抗變-介面只能把泛型型別T用作其方法的輸入
  public interface IDisplay<in T>
  {
    void Show(T item);
  }
}

namespace Wrox.ProCSharp.Generics
{
  // covariant
  //泛型介面的協變-返回型別只能是T
  public interface IIndex<out T>
  {
    T this
 
[int index] { get; }
    int Count { get; }
  }
}

using System;

namespace Wrox.ProCSharp.Generics
{
  public class RectangleCollection : IIndex<Rectangle>
  {
    private Rectangle[] data = new Rectangle[3] 
    {
      new Rectangle { Height=2, Width=5 },
      new Rectangle { Height=3, Width=7
 
},
      new Rectangle { Height=4.5, Width=2.9}
    };

    private static RectangleCollection coll;
    public static RectangleCollection GetRectangles()
    {
      return coll ?? (coll = new RectangleCollection());
    }

    public Rectangle this[int index]
    {
      get
      {
        if (index < 0 || index > data.Length)
          throw new ArgumentOutOfRangeException("index");
        return data[index];
      }
    }
    public int Count
    {
      get
      {
        return data.Length;
      }
    }
  }
}

using System;

namespace Wrox.ProCSharp.Generics
{
  public class ShapeDisplay : IDisplay<Shape>
  {
    public void Show(Shape s)
    {
      Console.WriteLine("{0} Width: {1}, Height: {2}", s.GetType().Name, s.Width, s.Height);
    }
  }
}

using System;

namespace Wrox.ProCSharp.Generics
{
  class Program
  {
    static void Main()
    {
      IIndex<Rectangle> rectangles = RectangleCollection.GetRectangles();
      IIndex<Shape> shapes = rectangles;

      for (int i = 0; i < shapes.Count; i++)
      {
        Console.WriteLine(shapes[i]);
      }


      IDisplay<Shape> shapeDisplay = new ShapeDisplay();
      IDisplay<Rectangle> rectangleDisplay = shapeDisplay;
      rectangleDisplay.Show(rectangles[0]);

    }

  }
}