As a nice follow-up to my last blog post…
C# also has a new feature called “contravariance” which allows you to define a delegate parameter with a derived type which will also allow you to pass types higher up in the inheritance chain. For example, if type X is a base class and type Y derives from X, you can define a delegate with a parameter of type Y and the delegate will also accept type X as a parameter.
using System;
class Automobile {
public static void PrintAutoParts(Automobile a) { }
}
class Car : Automobile {
public static void PrintCarParts(Car c) { }
}
class Application {
public delegate void PrintPartsList(Car car);
public static void Foo(PrintPartsList del) {}
public static void Main() {
PrintPartsList del1 = new PrintPartsList(Automobile.PrintAutoParts);
PrintPartsList del2 = new PrintPartsList(Car.PrintCarParts);
Foo(del1);
Foo(del2);
}
}
