C# Delegate Covariance

C# Delegate Covariance for beginners and professionals with examples on overloading, method overriding, inheritance, aggregation, base, polymorphism, sealed, abstract, interface, namespaces, exception handling, file io, collections, multithreading, reflection etc.

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C# Delegates Covariance

C# Delegate Covariance allows us to call a method that has derived return type of the delegate signature return type.

It means we can call a method that returns parent or child class object.

Here, we are creating two examples. First example calls a method that returns a parent or derived class object.

C# Delegate Covariance Example 1

using System;
namespace CSharpFeatures
{
    class A { }
    class B : A { }
    class DelegateCoveriance
    {
        delegate A Mydelegate();
        static void Main(string[] args)
        {
            // Calling MethodA
            Mydelegate del = MethodA;
            del();
            // Calling MethodB
            Mydelegate del2 = MethodB;
            del2();
        }
        static A MethodA()
        {
            Console.WriteLine("This is MethodA");
            return new A();
        }
        static B MethodB()
        {
            Console.WriteLine("This is MethodB");
            return new B();
        }
    }
}

Output:

This is MethodA
This is MethodB

C# Delegate Covariance Example 2

In this example, we are calling a method that does not return derived object as specified in delegate signature. Let's see what happen, if we do this.

using System;
namespace CSharpFeatures
{
    class A { }
    class B : A { }
    class C { }
    class DelegateCoveriance
    {
        delegate A Mydelegate();
        static void Main(string[] args)
        {
			// Delegating MethodA
            Mydelegate del = MethodA;
            del();
            // Delegating MethodB
            Mydelegate del2 = MethodB;
            del2();
            Mydelegate del3 = MethodC;
            del3();
        }
		static A MethodA()
        {
            Console.WriteLine("This is MethodA");
            return new A();
        }
		static B MethodB()
        {
            Console.WriteLine("This is MethodB");
            return new B();
        }
		static C MethodC()
        {
            Console.WriteLine("This is MethodC");
        }
    }
}

Output:

DelegateCoveriance.cs(25,31): error CS0407: 
'CSharpFeatures.C CSharpFeatures.DelegateCoveriance.MethodC()' has the wrong return type

Next TopicC# Delegate Inference

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