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In class-based programming, downcasting, or type refinement, is the act of casting a base or parent class reference, to a more restricted derived class reference. [1] This is only allowable if the object is already an instance of the derived class, and so this conversion is inherently fallible.
The overridden base method must be virtual, abstract, or override. In addition to the modifiers that are used for method overriding, C# allows the hiding of an inherited property or method. This is done using the same signature of a property or method but adding the modifier new in front of it. [6] In the above example, hiding causes the following:
The simplest example of type introspection in Java is the instanceof [1] operator. The instanceof operator determines whether a particular object belongs to a particular class (or a subclass of that class, or a class that implements that interface). For instance:
In the Java virtual machine, internal type signatures are used to identify methods and classes at the level of the virtual machine code. Example: The method String String. substring (int, int) is represented in bytecode as Ljava / lang / String. substring (II) Ljava / lang / String;. The signature of the main method looks like this: [2]
Multiple dispatch or multimethods is a feature of some programming languages in which a function or method can be dynamically dispatched based on the run-time (dynamic) type or, in the more general case, some other attribute of more than one of its arguments. [1]
For example, the Document Object Model (DOM) is a collection of objects that represent a page in a web browser, used by script programs to examine and dynamically change the page. There is a Microsoft Excel object model [1] for controlling Microsoft Excel from another program, and the ASCOM Telescope Driver is an object model for controlling an ...
The problem is that more than one degree of polymorphism exist: one for dispatching the display_on method to an object and another for selecting the right code (or method) for displaying. A much cleaner and more maintainable solution is then to do a second dispatch, this time for selecting the right method for displaying the object on the medium:
Impredicative polymorphism (also called first-class polymorphism) is the most powerful form of parametric polymorphism. [1]: 340 In formal logic, a definition is said to be impredicative if it is self-referential; in type theory, it refers to the ability for a type to be in the domain of a quantifier it contains. This allows the instantiation ...