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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 ...
Polymorphism can be distinguished by when the implementation is selected: statically (at compile time) or dynamically (at run time, typically via a virtual function). This is known respectively as static dispatch and dynamic dispatch, and the corresponding forms of polymorphism are accordingly called static polymorphism and dynamic polymorphism.
Polymorphism is the phenomenon wherein somewhat interchangeable objects each expose an operation of the same name but possibly differing in behavior. As an example, a File object and a Database object both have a StoreRecord method that can be used to write a personnel record to storage. Their implementations differ.
For the code to function as before, a decryption function is added to the code. When the code is executed, this function reads the payload and decrypts it before executing it in turn. Encryption alone is not polymorphism. To gain polymorphic behavior, the encryptor/decryptor pair is mutated with each copy of the code.
We then iterate over one of the lists (SHAPE), allowing elements of the other (SURFACE) to visit each of them in turn. In the example code above, SURFACE objects are visiting SHAPE objects. The code makes a polymorphic call on {SURFACE}.draw indirectly by way of the `drawing_agent', which is the first call (dispatch) of the double-dispatch pattern.
The indirection pattern supports low coupling and reuses potential between two elements by assigning the responsibility of mediation between them to an intermediate object. An example of this is the introduction of a controller component for mediation between data (model) and its representation (view) in the model-view-controller pattern.
The following example is in the language Java, and shows how the contents of a tree of nodes (in this case describing the components of a car) can be printed. Instead of creating print methods for each node subclass ( Wheel , Engine , Body , and Car ), one visitor class ( CarElementPrintVisitor ) performs the required printing action.
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 ...