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Can a generic interface extend a contravariant interface?
The same rule is applied to contravariant generic type parameters. You can create an interface that extends both the interface where the generic type parameter T is covariant and the interface where it is contravariant if in the extending interface the generic type parameter T is invariant. This is illustrated in the following code example.
How to implement a variant interface in a class?
You implement variant generic interfaces in classes by using the same syntax that is used for invariant interfaces. The following code example shows how to implement a covariant interface in a generic class. Classes that implement variant interfaces are invariant. For example, consider the following code. // The interface is covariant.
Is the generic type parameter in iinvariant invariant?
In the IInvariant interface, the generic type parameter T is invariant, whereas in IExtCovariant the type parameter is covariant, although both interfaces extend the same interface. The same rule is applied to contravariant generic type parameters.
What’s the difference between covariance and contravariance in Java?
Covariance allows interface methods to have more derived return types than that defined by the generic type parameters. Contravariance allows interface methods to have argument types that are less derived than that specified by the generic parameters. A generic interface that has covariant or contravariant generic type parameters is called variant.
How to declare generic type parameters in interfaces?
You can declare generic type parameters in interfaces as covariant or contravariant. Covariance allows interface methods to have more derived return types than that defined by the generic type parameters. Contravariance allows interface methods to have argument types that are less derived than that specified by the generic parameters.
How to create generic interfaces in Visual Basic?
You can create an interface that extends both the interface where the generic type parameter T is covariant and the interface where it is contravariant if in the extending interface the generic type parameter T is invariant. This is illustrated in the following code example.
Can a generic class implement a closed constructed interface?
Generic classes can implement generic interfaces or closed constructed interfaces as long as the class parameter list supplies all arguments required by the interface, as follows: