public void GenericityContravariant()
{
// 直接声明Animal类
Animal animal = new Animal();
Console.WriteLine($"{animal.GetType()}");
// 直接声明Cat类
Cat cat = new Cat();
Console.WriteLine($"{cat.GetType()}");
// 声明子类对象指向父类
Animal animal2 = new Cat();
Console.WriteLine($"{animal2.GetType()}");
// 声明Animal类的集合
List <Animal> listAnimal = new List <Animal>();
foreach (var item in listAnimal)
{
Console.WriteLine($"{item.GetType()}");
}
// 声明Cat类的集合
List <Cat> listCat = new List <Cat>();
foreach (var item in listCat)
{
Console.WriteLine($"{item.GetType()}");
}
ICustomerListIn <Cat> customerListCat1 = new CustomerListIn <Cat>();
Console.WriteLine($"{customerListCat1.GetType()}");
ICustomerListIn <Cat> customerListCat2 = new CustomerListIn <Animal>();
Console.WriteLine($"{customerListCat2.GetType()}");
Assert.IsTrue(true);
}
public void Tshow()
{
//协变：接口泛型参数加了个out，就是为了解决上述的问题
{
ICustomerListOut <Bird> customerList2 = new CustomerListOut <Sparrow>();
customerList2.Get();/*有返回值*/
}
//逆变
{
ICustomerListIn <Sparrow> customerList1 = new CustomerListIn <Bird>();
customerList1.Show(new Sparrow()
{
Id = 1, Name = "张三"
}); /*有参数*/
}
{
IMyList <Sparrow, Bird> myList2 = new MyList <Sparrow, Sparrow>(); //协变
IMyList <Sparrow, Bird> myList3 = new MyList <Bird, Bird>(); //逆变
IMyList <Sparrow, Bird> myList4 = new MyList <Bird, Sparrow>(); //协变+逆变
}
}
public static void Show()
{
{
Bird parent1 = new Bird();
Bird parent2 = new Sparrow();
Sparrow child = new Sparrow();
}
{
List <Bird> birdList = new List <Bird>();
//List<Bird> birdList1 = new List<Sparrow>();//两个list泛型实例不存在继承关系,
//每只麻雀都是一只鸟，但是list不知道，需要强制去转
List <Bird> birdList2 = new List <Sparrow>().Select(c => (Bird)c).ToList();//把每一只麻雀转换为bird
}
{
IEnumerable <Bird> birdList1 = new List <Bird>();
IEnumerable <Bird> birdList2 = new List <Bird>();
}
{
ICustomerListOut <Bird> customerList = new CustomerListOut <Bird>();
ICustomerListOut <Bird> customerList1 = new CustomerListIn <Sparrow>();
}
}
