Slide 1

Arrays Covariance

In C#, covariance and contravariance enable implicit reference conversion for array types, delegate types, and generic type arguments. Covariance preserves assignment compatibility and contravariance reverses it.

Covariance for arrays enables implicit conversion of an array of a more derived type to an array of a less derived type. But this operation is not type safe, as shown in the following code example.

 object[] array = new String[10];  
 // The following statement produces a run-time exception.  
 // array[0] = 10; 

Slide 2

Covariance and contravariance support for method groups allows for matching method signatures with delegate types. This enables you to assign to delegates not only methods that have matching signatures, but also methods that return more derived types (covariance) or that accept parameters that have less derived types (contravariance) than that specified by the delegate type.

In .NET Framework 4 and later versions, C# supports covariance and contravariance in generic interfaces and delegates and allows for implicit conversion of generic type parameters.

Ref:- https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/covariance-contravariance/