委托的协变与逆变代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public delegate T Function<out T>();    //泛型委托   out关键字:基于协变的变体
    //public delegate Strong Function2();     //普通委托
    public delegate void Operate<in T>(T instance);//泛型委托   in关键字:基于逆变的变体

    public class Program
    {
        static void Main(string[] args)
        {
            //协变委托
            Function<Strong> funStrong = new Function<Strong>(GetInstance);
            Function<Weak> funWeak = funStrong;
            Weak weak = funWeak();

            //逆变委托
            Operate<Weak> opWeak = new Operate<Weak>(DoSth);
            Operate<Strong> opStrong = opWeak;
            opStrong(new Strong());
        }

        static Strong GetInstance()
        {
            return new Strong();
        }

        static void DoSth(Weak weak) { 
            //...
        }
    }

    /// <summary>
    /// 强类型
    /// </summary>
    class Weak { }

    /// <summary>
    /// 弱类型
    /// </summary>
    class Strong : Weak
    { 
    
    }
}