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Dynamic dispatch contrasts with static dispatch, in which the implementation of a polymorphic operation is selected at compile time. The purpose of dynamic dispatch is to defer the selection of an appropriate implementation until the run time type of a parameter (or multiple parameters) is known.
In computing, late binding or dynamic linkage [1] —though not an identical process to dynamically linking imported code libraries—is a computer programming mechanism in which the method being called upon an object, or the function being called with arguments, is looked up by name at runtime.
Languages that separate the programmatic interface of objects from the implementation, like Visual Basic and Delphi, also tend to use this approach, because it allows objects to use a different implementation simply by using a different set of method pointers. The method allows creation of external libraries, where other techniques perhaps may not.
Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should favor polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) over inheritance from a base or parent class. [2]
The Microsoft Implementation of CRTP in Active Template Library (ATL) was independently discovered, also in 1995, by Jan Falkin, who accidentally derived a base class from a derived class. Christian Beaumont first saw Jan's code and initially thought it could not possibly compile in the Microsoft compiler available at the time.
The concept of the virtual function solves the following problem: In object-oriented programming, when a derived class inherits from a base class, an object of the derived class may be referred to via a pointer or reference of the base class type instead of the derived class type.
This is done by using traditional polymorphism while also casting the argument to dynamic. [3] The run-time binder will choose the appropriate method overload at run-time. This decision will take into consideration the run-time type of the object instance (polymorphism) as well as the run-time type of the argument.
This is a generalization of single-dispatch polymorphism where a function or method call is dynamically dispatched based on the derived type of the object on which the method has been called. Multiple dispatch routes the dynamic dispatch to the implementing function or method using the combined characteristics of one or more arguments.