/// <summary>
/// 协变测试
/// 1.协变类型参数，该参数只能用于输出的位置（例如方法的返回值）
/// 2.仅泛型接口和泛型委托支持协变类型参数（泛型类不支持协变类型参数）
/// 在接口和委托的类型参数上指定out修饰符可将其声明为协变参数
/// 3.（由于历史原因）数组支持协变
/// </summary>
private void Test01()
{
MyStackA <Cat> catStack = new MyStackA <Cat>();
//MyStackA<Animal> animalStack = catStack;//编译报错
MyStackB <Cat> catStackB = new MyStackB <Cat>();
IPoppable <Animal> animalStackB = catStackB;//利用协变
Animal a1 = animalStackB.Pop();
//WashA(catStackB);
//WashB(catStackB);
WashC(catStackB);
}
private static void GenericTypesTests()
{
Console.WriteLine("--- {0} ---", System.Reflection.MethodBase.GetCurrentMethod().Name);
Stack <int> stack = new Stack <int>();
stack.Push(5);
stack.Push(10);
int x = stack.Pop();
int y = stack.Pop();
int xx = 5, yy = 10;
Generics.Swap(b: ref yy, a: ref xx);
Type g1 = typeof(G <>);
Type g2 = typeof(G <,>);
Console.WriteLine(g2.GetGenericArguments().Count());
Type g3 = typeof(G <int, int>);
Console.WriteLine(g3.GetGenericArguments().Count());
Console.WriteLine(++Bob <int> .Count);
Console.WriteLine(++Bob <int> .Count);
Console.WriteLine(++Bob <string> .Count);
Console.WriteLine(++Bob <object> .Count);
// Covariance
{
// Assuming that Bear subclasses Animal:
var bears = new Stack <Bear>();
bears.Push(new Bear());
// Because bears implements IPoppable<Bear>, we can convert it to IPoppable<Animal>:
IPoppable <Animal> animals = bears; // Legal
Animal a = animals.Pop();
}
// Contravariance
{
IPushable <Animal> animals = new Stack <Animal>();
IPushable <Bear> bears = animals; // Legal
bears.Push(new Bear());
}
Console.WriteLine("=====================================================================");
}
static void Main(string[] args)
{
// Stack covariance
Animal animal = new Bear(); // Bear is convertible to Animal (asumption above)
var bearStack = new Stack <Bear>();
bearStack.Push(animal as Bear);
bearStack.Push(new Bear());
IPoppable <Animal> animalPop = bearStack;
animal = animalPop.Pop();
//Stack<Animal> animalst = bears; // not a covariant parameter, classes do not permit covariant paramters since data flow in both directions
ZooCleaner.Wash(bearStack); // OK, covariant method
// contravariance
var animalStack = new Stack <Animal>();
IPushable <Bear> bearPush = animalStack; // legal
IPushable <Camel> camelPush = animalStack; // legal, contravariant
animalStack.Push(new Bear());
animalStack.Push(new Camel());
camelPush.Push(new Camel());
bearPush.Push(new Bear());
// Interface covariance
string s = "Hello";
object o = s;
IFoo <string> fooString = new FooString();
//IFoo<object> fooObject; fooObject = fooString; // HEY! interfaces should be covariant!!!! Whats up?
// Array covariance
Bear[] bearArr = new Bear[] { new Bear(), new Bear() };
Animal[] animalArr = bearArr; // OK, covariant
animalArr[1] = new Bear();
//animalArr[1] = new Camel(); ArrayTypeMismatchException: Attempted to access an element as a type incompatible with the array.
//animalArr[1] = new Animal(); ditto
}
private void OnBubbleTap(IPoppable bubble)
{
bubble.Pop();
OnBubblePoped?.Invoke(bubble.GetScore());
}