泛型-协变

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

namespace 专高四
{
    class 协变
    {
        static void Main_协变()
        {
            Stacks<Bear> bears = new Stacks<Bear>();
            bears.Push(new Bear());

            Stacks<Camal> camals = new Stacks<Camal>();
            camals.Push(new Camal());

            IStacks<Animal> animal = bears;
            animal = camals;

            //Stacks<Bear, Animal> bear = new Stacks<Bear, Animal>();
            //IStacks2<Bear, Animal> zoo = bear;
        }
    }

    /*协变：参数传进的是子类，方法返回的是父类，表示父类一定拥有子类的属性，最终一定可以转换*/
    /*逆变：参数外部传进的是父类，方法体内用的是子类，表示方法体的子类继承自参数的父类。*/

    public interface IStacks<out T1>
    {
        T1 Pop();
    }

    public interface IStacks2<in T1, out T2> where T1 : class
    {
        T2 Pop();

        void Push(T1 obj);
    }

    public class Stacks<T1> : IStacks<T1>
    {
        T1[] list = new T1[100];

        int index;
        public T1 Pop()
        {
            return list[--index];
        }

        public void Push(T1 obj)
        {
            list[index++] = obj;
        }
    }

    public class Stacks<T1, T2> : IStacks2<T1, T2>
        where T1 : class
        where T2 : class
    {
        T2[] list = new T2[100];

        int index;
        public T2 Pop()
        {
            return list[--index];
        }

        public void Push(T1 obj)
        {
            list[++index] = obj as T2;
        }
    }


    class Animal
    {

    }

    class Bear : Animal
    {

    }

    class Camal : Animal
    {

    }

}

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

namespace 专高四
{
    class 泛型
    {
        static void Main()
        {
            Stacks<string> s = new Stacks<string>();
            s.Push("a");
            s.Push("b");
            s.Push("c");

            Console.WriteLine("{0,-11}{1,-11}{2,-11}", s.Pop(), s.Pop(), s.Pop());

            ObjHelper<Student> obj = new ObjHelper<Student>();
            Student stu1 = new Student { Id = 1, Name = "xiao" };
            var stu2 = obj.Clone(stu1);
            
            Console.WriteLine(stu2.Id);
        }
    }

    public class ObjHelper<T>
        where T : new()
    {
        public T Clone(T obj)
        {
            T t = new T();
            t = obj;
            return t;
        }        
    }

    
}