private void ContravarianceExample()
{
ConsoleExtensions
.WriteColoredLine(Resources.ContravarianceExampleRunning, ConsoleColor.Cyan);
// A contravariant type in an interface or delegate can be converted to a more SPECIFIC
// type.
// Interface: IContravariant<Fruit> to IContravariant<Apple>
IContravariant <Apple> appleContravariantInterface = this.fruitContravariantInterface;
// Delegate: Contravariant<Fruit> to Contravariant<Orange>
Contravariant <Orange> orangeContravariantDelegate =
this.fruitContravariantDelegate;
const int AppleQuality = 75;
const int OrangeQuality = 60;
var appleValue = appleContravariantInterface.GetValue(
new Apple(AppleColor.Red, AppleQuality));
var orangeValue = orangeContravariantDelegate(new Orange(OrangeQuality));
Console.WriteLine(
Resources.ContravarianceExampleAppleValue,
nameof(appleValue),
appleValue);
Console.WriteLine(
Resources.ContravarianceExampleOrangeValue,
nameof(orangeValue),
orangeValue);
Console.WriteLine();
}
public void Contravariance()
{
IContravariant <Fruit> fruit = new Contravariant <Fruit>();
IContravariant <Apple> apple = new Contravariant <Apple>();
Contravariant(fruit); //fruit is being downcasted to apple, without the in keyword this will not compile
Contravariant(apple);
}
private static void Contravariance()
{
IContravariant <Apple> fruit = new Contravariant <Fruit>();
IContravariant <Apple> apple = new Contravariant <Apple>();
// IContravariant<Fruit> apple = new Contravariant<Apple>(); // not allowed
Console.WriteLine(fruit.GetType());
Console.WriteLine(apple.GetType());
}
static void ContravariantAndCovariant()
{
IContravariant <BaseClass> iBaseClassA = new Contravariant <BaseClass>();
iBaseClassA.Method(new DerivedClass());
ICovariant <BaseClass> iBaseClassB = new Covariant <BaseClass>();
iBaseClassB.Method().Print();
}
static void Run()
{
ICovariant <Fruit> apple = new Covariant <Apple>(); //because it's covariant
IContravariant <Apple> fruit = new Contravariant <Fruit>(); //because it's contravariant
}