一，泛型接口中泛型类型的前面标有in和out关键字 其中标有out关键字的参数我协变，而输出的结果就是抗变，IN与之相反。
如下代码：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace KongzhiTai
{
class Program
{
static void Main(string[] args)
{
//IIndex<Rectangle> rectangles = RectangleCollection.Getrectangles();//
//IIndex<Shape> shapes = rectangles;
//for (var i = 0; i < shapes.Count; i++)
//{
// Console.WriteLine(shapes[i]);
//}
//Console.ReadKey();
Rectangle re = new Rectangle();
re.Heigh = 11;
re.Width = 11;
Console.WriteLine(re);
Console.ReadKey();
}
}
//创建实现接口 IIndex的RectangleCollection类
public class RectangleCollection : IIndex<Rectangle>
{
//创建rectangle集合
private readonly Rectangle[] _data = new Rectangle[3]
{
new Rectangle{Heigh=11,Width=11},
new Rectangle{Heigh=22,Width=22},
new Rectangle{Heigh=33,Width=33}
};
public static RectangleCollection Getrectangles()
{
return new RectangleCollection();
}
public Rectangle this[int index]
{
get { return _data[index]; }
}
//创建的rectangle的长度
public int Count
{
get { return _data.Length; }
}
}
//如果泛型类型用out关键字标注，泛型接口就是协变的。这也意味着返回类型只能是T
public interface IIndex<out T>
{
T this[int index] { get; }//返回值是T类型的索引器
int Count { get; }//Count属性
}
public class Shape
{
public double Heigh { get; set; }
public double Width { get; set; }
public override string ToString()
{
return string.Format("Width:{0},Height:{1}", Width.ToString(), Heigh.ToString());
}
}
public class Rectangle : Shape
{
}
}