static void Main(string[] args)
{
var del1 = new CovariantDelegate <MyParentType>(MyStaticMethodWithReturnParentType);
var del2 = new CovariantDelegate <MyParentType>(MyStaticMethodWithReturnChildType);
// Error
//var del3 = new CovariantDelegate<MyChildType>(MyStaticMethodWithReturnParentType);
var del4 = new CovariantDelegate <MyChildType>(MyStaticMethodWithReturnChildType);
var del5 = new ContravariantDelegate <MyParentType>(MyStaticMethodWithInParentType);
// Error
//var del6 = new ContravariantDelegate<MyParentType>(MyStaticMethodWithInChildType);
var del7 = new ContravariantDelegate <MyChildType>(MyStaticMethodWithInParentType);
var del8 = new ContravariantDelegate <MyChildType>(MyStaticMethodWithInChildType);
del1();
del2.Invoke();
del4();
del5(new MyParentType());
del7(new MyChildType());
del8(new MyChildType());
var myType = new MyType();
var del9 = new CovariantDelegate <MyParentType>(myType.MyMethodWithReturnParentType);
var del10 = new CovariantDelegate <MyParentType>(myType.MyMethodWithReturnChildType);
del9();
del10();
Console.ReadLine();
}
static void Main(string[] args)
{
#region 泛型调用
//泛型委托
InputGenericsDelegate <int> inputGenericsDelegate = (p) => { Console.WriteLine("泛型委托"); };
//泛型类
MyGenerics <string> myGenerics = new MyGenerics <string>();
//泛型方法
myGenerics.GenericsMethod <string>("泛型方法");
myGenerics.GenericsMethod <string, int>("泛型方法");
#endregion
#region 泛型可变性
//协变
CovariantDelegate <string> covariantDelegateStr = () => { return("协变泛型委托"); };
CovariantDelegate <object> covariantDelegate = covariantDelegateStr;
//逆变
ContravariantDelegate <object> contravariantDelegateObj = (p) => { Console.WriteLine("逆变泛型委托"); };
ContravariantDelegate <string> contravariantDelegate = contravariantDelegateObj;
#endregion
Console.ReadKey();
}
//https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/covariance-contravariance/using-variance-in-delegates
//https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/covariance-contravariance/using-variance-for-func-and-action-generic-delegates
static void Main(string[] args)
{
//Delegate Covariance / Contrvariance
{
Action <A> f1 = ProcessA;
//Contrvariance - function which accepts less derived type, can be assigned to more derived type delegate
//All Action delegate are contrvariant
Action <B> f2 = f1;
ContrvariantDelegate <A> f3 = ProcessA;
//Direct contrvariant assignment is always supported (because it is basically wrapping in new Action())
ContrvariantDelegate <B> f5 = ProcessA;
//This won't compile if "in" keyword is missing in Delegate definition
ContrvariantDelegate <B> f6 = f3;
CovariantDelegate <B> f7 = ReturnB;
//Direct covariant assignment is always supported (because it is basically wrapping in new Action())
CovariantDelegate <A> f8 = ReturnB;
//This won't compile if "out" keyword is missing in Delegate definition
CovariantDelegate <A> f9 = f7;
}
//Collection Invariance
//Those lines won't compile
//List<A> list = new List<B>();
//IList<A> list1 = new List<B>();
//IEnumerable though supports covariance because you can not change it
var list2 = new List <B>();
IEnumerable <A> list3 = list2;
//Arrays support variance but can emmit runtime exception
A[] array = new B[1];
//Like in this case
array[0] = new A();
//Interface Covariance Contrvariance
//https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/covariance-contravariance/creating-variant-generic-interfaces
ICovariant <B> interfaceExample = null;
//This won't compile without "out" keyword
ICovariant <A> i = interfaceExample;
IContrvariant <A> interfaceExample2 = null;
//This won't compile without "in" keyword
IContrvariant <B> i2 = interfaceExample2;
//Accepts A, returns B
IGenericInterface <A, B> interfaceExample3 = null;
//Accepts B, returns A
IGenericInterface <B, A> i3 = interfaceExample3;
//Basically Contrvariance allows to accept more derived arguments and covariance to return less derived arguments
}
static void Main1(string[] args)
{
Planet p = new Planet();
Earth e = new Earth();
CovariantDelegate varCovariantDelegate = new CovariantDelegate(p.CallingPlanet);
varCovariantDelegate();
varCovariantDelegate = new CovariantDelegate(e.CallingEarth);
varCovariantDelegate();
ContravariantDelegate varContravariantDelegate = new ContravariantDelegate(PlanetParamMethod);
varContravariantDelegate(e);
varContravariantDelegate = new ContravariantDelegate(EarthParamMethod);
varContravariantDelegate(e);
}