// Initialize delegate variables.
public void RunCovarianceAndContravarianceDelegates()
{
// Use covariance to set ReturnPersonMethod = ReturnEmployee.
ReturnPersonMethod = ReturnEmployee;
// Use contravariance to set EmployeeParameterMethod = PersonParameter.
EmployeeParameterMethod = PersonParameter;
}
// Initialize delegate variables.
private void Form1_Load(object sender, EventArgs e)
{
// Set ReturnPersonMethod = ReturnEmployee.
// Covariance allows this because ReturnPersonDelegate
// returns a Person and an Employee is a kind of Person.
ReturnPersonMethod = ReturnEmployee;
// Set EmployeeParameterMethod = PersonParameter.
// Contravariance allows this because EmployeeParameterDelegate
// takes an Employee as a parameter and an Employee is a kind of Person.
// In other words, when you invoke the delegate's method you will
// pass it an Employee and an Employee is a kind of Person so
// PersonParameter can handle it.
EmployeeParameterMethod = PersonParameter;
}
// Initialize delegate variables.
private void Form1_Load(object sender, EventArgs e)
{
// Set ReturnPersonMethod = ReturnEmployee.
// Covariance allows this because ReturnPersonDelegate
// returns a Person and an Employee is a kind of Person.
ReturnPersonMethod = ReturnEmployee;
// Set EmployeeParameterMethod = PersonParameter.
// Contravariance allows this because EmployeeParameterDelegate
// takes an Employee as a parameter and an Employee is a kind of Person.
// In other words, when you invoke the delegate's method you will
// pass it an Employee and an Employee is a kind of Person so
// PersonParameter can handle it.
EmployeeParameterMethod = PersonParameter;
}
private static void Main(string[] args)
{
// Set ReturnPersonMethod = ReturnEmployee.
// Covariance allows this because ReturnPersonDelegate
// returns a Person and an Employee is a kind of Person.
ReturnPersonMethod = ReturnEmployee;
// Set EmployeeParameterMethod = PersonParameter.
// Contravariance allows this because EmployeeParameterDelegate
// takes an Employee as a parameter and an Employee is a kind of Person.
// In other words, when you invoke the delegate's method you will
// pass it an Employee and an Employee is a kind of Person so
// PersonParameter can handle it.
EmployeeParameterMethod = PersonParameter;
}
static void Main()
{
//Covariance
Console.WriteLine("Vanilla Covariance");
ReturnPersonMethod = ReturnEmployee;
ReturnPersonMethod();
Console.WriteLine();
//Func Covariance
Console.WriteLine("Func Covariance");
ReturnPersonFunc = ReturnEmployee;
ReturnPersonFunc();
Console.WriteLine();
//Contravariance
Console.WriteLine("Vanilla Contravariance");
EmployeeParameterMethod = SomethingThatTakesAPerson;
EmployeeParameterMethod(new Employee());
Console.WriteLine();
//Action contravariance
Console.WriteLine("Action Contravariance");
EmployeeParameterAction = SomethingThatTakesAPerson;
EmployeeParameterAction(new Employee());
Console.WriteLine();
//ContraCovariance
Console.WriteLine("Vanilla ContraCovariance");
ReturnsPersonTakesEmployeeMethod = ReturnsEmployeeTakesPerson;
ReturnsPersonTakesEmployeeMethod(new Employee());
Console.WriteLine();
//Anonymous Method
Console.WriteLine("Anonymous Method");
Console.WriteLine(SomeFunction(2, 3));
Console.ReadLine();
}
/// <summary>
/// Contravariance lets a method take parameters that are from a superclass of the type expected by a delegate.
/// </summary>
void ContravarianceExample()
{
employeeParameterMethod = PersonParameter;
}
