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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 computer programming, a virtual method table (VMT), virtual function table, virtual call table, dispatch table, vtable, or vftable is a mechanism used in a programming language to support dynamic dispatch (or run-time method binding).
With the C Object System library, [19] C does support dynamic dispatch similar to CLOS. It is fully extensible and does not need any manual handling of the methods. Dynamic message (methods) are dispatched by the dispatcher of COS, which is faster than Objective-C. Here is an example in COS:
This is known respectively as static dispatch and dynamic dispatch, and the corresponding forms of polymorphism are accordingly called static polymorphism and dynamic polymorphism. Static polymorphism executes faster, because there is no dynamic dispatch overhead, but requires additional compiler support.
The call is therefore subject to all the usual additional performance costs that are associated with dynamic resolution of calls, usually more than in a language supporting only single method dispatch. In C++, for example, a dynamic function call is usually resolved by a single offset calculation - which is possible because the compiler knows ...
This contrasts with dynamic dispatch, which is based on runtime information (such as vtable pointers and other forms of run time type information). Static dispatch is possible because there is a guarantee of there only ever being a single implementation of the method in question.
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OWL 1.0 depended on Dynamic Dispatch Virtual Tables (DDVT), a proprietary extension to C++ that allowed the programmer to bind Windows messages (events) to functions (event handlers) in a simple manner and with little run-time overhead. MFC, on the other hand, used a solution that did not require a language extension.