static void Main(string[] args)
{
Vehicle vehicle1 = new Vehicle(); //ok
Bus bus1 = new Bus(); //ok
Console.WriteLine("***Exploring Contravariance with C# delegates***");
//General case
TakingDerivedTypeParameterDelegate del1 = bus1.ShowBus;
del1(bus1);
//Special case:
//Contravariance:
//Note that the delegate expected a method that accepts a bus(derived) object parameter
//but still it can point to the method that accepts vehicle(base) object parameter
TakingDerivedTypeParameterDelegate del2 = vehicle1.ShowVehicle;
del2(bus1);
//Additional note:you cannot pass vehicle object here
//del2(vehicle1);//error
Console.ReadKey();
}
static void Main(string[] args)
{
Vehicle vehicle1 = new Vehicle(); //ok
Bus bus1 = new Bus(); //ok
Console.WriteLine("***Exploring Contravariance with C# delegates * **");
//General case
TakingDerivedTypeParameterDelegate del1 = bus1.ShowBus;
del1(bus1);
//Special case:
//Contravariance:
/*Note that the delegate expected a method that accepts a
* bus(derived) object parameter but still it can point to the
* method that accepts vehicle(base) object parameter*/
TakingDerivedTypeParameterDelegate del2 = vehicle1.ShowVehicle; //重点！！！！
//一个接受Bus作为参数的委托可以指向一个接受其父类（Vehicle）作为参数的方法
del2(bus1); //但调用时需传入Bus对象，如果传入Vehicle对象会报错（因为signature不匹配）。
//Additional note:you cannot pass vehicle object here
//del2(vehicle1);//error
Mydel2 myDel2 = vehicle1.ShowVehicle;
Mydel2 myDel3 = bus1.ShowBus; //报错
//委托的参数是Vehicle，不能指向一个接受其子类Bus的方法！
//（否则，你使用这个委托时，只知道这个委托接受Vehicle，可能会传入不符合被指向的方法要求的参数）
//委托的返回类型如果是Vehicle的话，它可以指向一个返回类型是其子类Bus的方法（这里未演示）
Console.ReadKey();
}
