public static void Show()
{
{
Bird bird1 = new Bird();
Bird bird2 = new Sparrow();
Sparrow sparrow1 = new Sparrow();
// Sparrow sparrow2 = new Bird();
}
{
List <Bird> bird1 = new List <Bird>();
// 应该可以这样写， 一堆麻雀当然是一堆鸟
// 但是实际上不行。
// 因为 List<Bird> 和 List<Sparrow>
// 没有父子关系。
// List<Bird> bird2 = new List<Sparrow>();
List <Bird> birds3 = new List <Sparrow>().Select(c => (Bird)c).ToList();
}
{
// 协变
// 之所以可以这样写，是因为在泛型接口IEnumerable当中
// 在泛型类型前使用了out
// out 修饰后，泛型类型只能放在返回值而不能放在函数入参中
IEnumerable <Bird> birds1 = new List <Bird>();
IEnumerable <Bird> birds2 = new List <Sparrow>();
//委托
Func <Bird> func = new Func <Sparrow>(() => null);
ICustomerListOut <Bird> customerListOut = new CustomerListOut <Bird>();
ICustomerListOut <Bird> customerListOut2 = new CustomerListOut <Sparrow>();
}
{
// 逆变
ICustomerListIn <Sparrow> customerListIn1 = new CustomerListIn <Sparrow>();
ICustomerListIn <Sparrow> customerListIn2 = new CustomerListIn <Bird>();
ICustomerListIn <Bird> birds = new CustomerListIn <Bird>();
birds.Show(new Sparrow());
birds.Show(new Bird());
Action <Sparrow> act = new Action <Bird>((Bird i) => {});
}
{
IMyList <Sparrow, Bird> myList1 = new MyList <Sparrow, Bird>();
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>(); // 逆变 + 协变
}
}
public static void Show()
{
{
Bird bird1 = new Bird();
Bird bird2 = new Sparrow();
Sparrow sparrow1 = new Sparrow();
/* Sparrow sparrow2 = new Bird()*/
;
}
{
List <Bird> birdList1 = new List <Bird>();
//List<Bird> birdList2 = new List<Sparrow>();
//难道一组麻雀不是一组鸟吗？
//List<Bird> 是一个类， List<Sparrow> 是另外一个类，二者没有继承
List <Bird> birdList3 = new List <Sparrow>().Select(c => (Bird)c).ToList();
}
//泛型在使用的时候，会存在不和谐的地方
// 协变和逆变 都是在泛型中才有，在泛型接口 或者泛型委托才有
{//out修改类型参数，协变:可以让右边使用子类
// 使用协变时候，可以把子类放在右边，这才是泛型该有的样子
IEnumerable <Bird> birdList1 = new List <Bird>();
IEnumerable <Bird> birdList2 = new List <Sparrow>(); //为什么可以写？
ICustomerListOut <Bird> customerList1 = new CustomerListOut <Bird>();
ICustomerListOut <Bird> customerList2 = new CustomerListOut <Sparrow>();
}
{//逆变
//int修改类型参数，逆变:可以让右边使用父类
// 类型参数只能作为参数 ，不能作为返回值
ICustomerListIn <Sparrow> customerList2 = new CustomerListIn <Sparrow>();
ICustomerListIn <Sparrow> customerList1 = new CustomerListIn <Bird>();
customerList1.Show(new Sparrow());
ICustomerListIn <Bird> birdList1 = new CustomerListIn <Bird>();
birdList1.Show(new Sparrow());
birdList1.Show(new Bird());
}
{
IMyList <Sparrow, Bird> myList1 = new MyList <Sparrow, Bird>();
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
}
//完全能理清楚 刷个1
//能清楚80% 2 60% 3
}
public static void Show()
{
{
Bird bird1 = new Bird();
Bird bird2 = new Sparrow();
Sparrow sparrow1 = new Sparrow();
//Sparrow sparrow2 = new Bird();
}
{
List <Bird> birdList1 = new List <Bird>();
//List<Bird> birdList2 = new List<Sparrow>();
//应该可以呀 一堆麻雀当然是一堆鸟
//没有父子关系
List <Bird> birdList3 = new List <Sparrow>().Select(c => (Bird)c).ToList();
}
{//协变
IEnumerable <Bird> birdList1 = new List <Bird>();
IEnumerable <Bird> birdList2 = new List <Sparrow>();
Func <Bird> func = new Func <Sparrow>(() => null);
ICustomerListOut <Bird> customerList1 = new CustomerListOut <Bird>();
ICustomerListOut <Bird> customerList2 = new CustomerListOut <Sparrow>();
}
{//逆变
ICustomerListIn <Sparrow> customerList2 = new CustomerListIn <Sparrow>();
ICustomerListIn <Sparrow> customerList1 = new CustomerListIn <Bird>();
ICustomerListIn <Bird> birdList1 = new CustomerListIn <Bird>();
birdList1.Show(new Sparrow());
birdList1.Show(new Bird());
Action <Sparrow> act = new Action <Bird>((Bird i) => { });
}
{
IMyList <Sparrow, Bird> myList1 = new MyList <Sparrow, Bird>();
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>(); //逆变+协变
}
}