Covariant out and Contravariance in C #

Variability is often used in generic interfaces and generic delegates

In Contravariance, out covariant

From list<string> to list<object> called covariant (string derives from object, it is reasonable to turn a string into object, it is reasonable for subclasses to replace the parent class)

It is unreasonable to go from list<object> to List<string>, which is called inversion (by turning the object into a string and turning the parent class into a subclass, which is called inversion).

1. Invert Code Masking

  Static voidMain (string[] args) {Icovariant<Object> iobj =NewSample<object>(); Icovariant<String> ISTR =NewSample<string>(); //You can assign ISTR to Iobj because//The Icovariant interface is covariant. //iobj = ISTR;ISTR =iobj;//Convert from Object type to string type, parent class to subclass is Contravariant console.readline (); }        //covariant interface.        Interfaceicovariant<inchR> { }        //extending covariant interface.        Interfaceiextcovariant<inchR>: icovariant<r> { }        //implementing covariant interface.        classSample<r>: icovariant<r> {}

2. Co-change Demo

   Static voidMain (string[] args) {Icovariant<Object> iobj =NewSample<object>(); Icovariant<String> ISTR =NewSample<string>(); //You can assign ISTR to Iobj because//The Icovariant interface is covariant. //iobj = ISTR;Iobj =ISTR;            //From string to type Object, sub-type to parent (the Richter substitution principle) is covariant        Console.ReadLine (); }        //covariant interface.        Interfaceicovariant< outR> { }        //extending covariant interface.        Interfaceiextcovariant< outR>: icovariant<r> { }        //implementing covariant interface.        classSample<r>: icovariant<r> {}

Covariant out and Contravariance in C #