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. For more information, see Variance in Generic Interfaces (C#) and Variance in Delegates (C#).
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Which delegates support covariance and contravariance in C#?
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. For more information, see Variance in Generic Interfaces (C#) and Variance in Delegates (C#).
What is the difference between covariance and contravariance?
Covariance permits a method to have a return type that is a subtype of the one defined in the delegate. Contravariance permits a method to have a parameter type that is a base type of the one defined in the delegate type.
What is Contravariant C#?
C# Contravariance Cotravariance allows a method with the parameter of a base class to be assigned to a delegate that expects the parameter of a derived class.
What is the delegates in C#?
A delegate is a type that represents references to methods with a particular parameter list and return type. When you instantiate a delegate, you can associate its instance with any method with a compatible signature and return type. You can invoke (or call) the method through the delegate instance.
What is covariance and Contravariance in generics?
Covariance and contravariance are terms that refer to the ability to use a more derived type (more specific) or a less derived type (less specific) than originally specified. Generic type parameters support covariance and contravariance to provide greater flexibility in assigning and using generic types.
Can type parameters be used with interfaces?
When an interface is specified as a constraint on a type parameter, only types that implement the interface can be used. The following code example shows a SortedList class that derives from the GenericList class.
Can you be declared as contravariant?
A type can be declared contravariant in a generic interface or delegate only if it defines the type of a method’s parameters and not of a method’s return type. In , ref , and out parameters must be invariant, meaning they are neither covariant nor contravariant.
What is covariant programming?
Covariance means that a method can return a type that is derived from the delegate’s return type. Contra-variance means that a method can take a parameter that is a base of the delegate’s parameter type.
When we should use delegates in C#?
When to use delegates?
- These are used to represent or refer to one or more functions.
- These can only be used to define call-back methods.
- In order to consume a delegate, we need to create an object to delegate.
What is Reifiable type?
A reifiable type is a type whose type information is fully available at runtime. This includes primitives, non-generic types, raw types, and invocations of unbound wildcards.
Can interface be made as static?
Similar to Default Method in Interface, the static method in an interface can be defined in the interface, but cannot be overridden in Implementation Classes. To use a static method, Interface name should be instantiated with it, as it is a part of the Interface only.
Can I use interface as generic type?
As you learned, you can use interface as type. In the same way, generic interface can be used as type, as shown below. As you can see in the above example, by using generic interface as type, we can specify the data type of key and value. In the same way, as you learned, you can use interface as function type.
How do you declare a generic interface as Contravariant?
You can declare a generic type parameter contravariant by using the in keyword. The contravariant type can be used only as a type of method arguments and not as a return type of interface methods. The contravariant type can also be used for generic constraints.
Which is a covariant return type?
Covariant return type refers to return type of an overriding method. It allows to narrow down return type of an overridden method without any need to cast the type or check the return type. Covariant return type works only for non-primitive return types.
What is the difference between delegate and callback?
The calling class has a preferred function that it wants run called a callback. The calling class sets the delegate to it’s callback. The difference between a delegate and a callback is the perspective: The service class calls the delegate that is set to the calling classes callback.
What are reified generics?
Reified Generics is a generics system that makes generics type information available at runtime. C# is one language that supports Reified Generics natively, as opposed to Java’s Type-Erased Generics.