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Dynamic dispatch
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Dynamic dispatch
In computer science, dynamic dispatch is the process of selecting which implementation of a polymorphic operation (method or function) to call at run time. It is commonly employed in, and considered a prime characteristic of, object-oriented programming (OOP) languages and systems.
Object-oriented systems model a problem as a set of interacting objects that enact operations referred to by name. 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. A program holds a reference to an object which may be either a File object or a Database object. Which one it is may have been determined by a run-time setting, and at this stage, the program may not know or care which. When the program calls StoreRecord on the object, something needs to choose which behavior gets enacted. If one thinks of OOP as sending messages to objects, then in this example the program sends a StoreRecord message to an object of unknown type, leaving it to the run-time support system to dispatch the message to the right object. The object enacts whichever behavior it implements.
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.
Dynamic dispatch is different from late binding (also known as dynamic binding). Name binding associates a name with an operation. A polymorphic operation has several implementations, all associated with the same name. Bindings can be made at compile time or (with late binding) at run time. With dynamic dispatch, one particular implementation of an operation is chosen at run time. While dynamic dispatch does not imply late binding, late binding does imply dynamic dispatch, since the implementation of a late-bound operation is not known until run time.[citation needed]
The choice of which version of a method to call may be based either on a single object, or on a combination of objects. The former is called single dispatch and is directly supported by common object-oriented languages such as Smalltalk, C++, Java, C#, Objective-C, Swift, JavaScript, and Python. In these and similar languages, one may call a method for division with syntax that resembles
where the parameters are optional. This is thought of as sending a message named divide with parameter divisor to dividend. An implementation will be chosen based only on dividend's type (perhaps rational, floating point, matrix), disregarding the type or value of divisor.
By contrast, some languages dispatch methods or functions based on the combination of operands; in the division case, the types of the dividend and divisor together determine which divide operation will be performed. This is known as multiple dispatch. Examples of languages that support multiple dispatch are Common Lisp, Dylan, and Julia.
A language may be implemented with different dynamic dispatch mechanisms. The choices of the dynamic dispatch mechanism offered by a language to a large extent alter the programming paradigms that are available or are most natural to use within a given language.
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Dynamic dispatch AI simulator
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Dynamic dispatch
In computer science, dynamic dispatch is the process of selecting which implementation of a polymorphic operation (method or function) to call at run time. It is commonly employed in, and considered a prime characteristic of, object-oriented programming (OOP) languages and systems.
Object-oriented systems model a problem as a set of interacting objects that enact operations referred to by name. 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. A program holds a reference to an object which may be either a File object or a Database object. Which one it is may have been determined by a run-time setting, and at this stage, the program may not know or care which. When the program calls StoreRecord on the object, something needs to choose which behavior gets enacted. If one thinks of OOP as sending messages to objects, then in this example the program sends a StoreRecord message to an object of unknown type, leaving it to the run-time support system to dispatch the message to the right object. The object enacts whichever behavior it implements.
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.
Dynamic dispatch is different from late binding (also known as dynamic binding). Name binding associates a name with an operation. A polymorphic operation has several implementations, all associated with the same name. Bindings can be made at compile time or (with late binding) at run time. With dynamic dispatch, one particular implementation of an operation is chosen at run time. While dynamic dispatch does not imply late binding, late binding does imply dynamic dispatch, since the implementation of a late-bound operation is not known until run time.[citation needed]
The choice of which version of a method to call may be based either on a single object, or on a combination of objects. The former is called single dispatch and is directly supported by common object-oriented languages such as Smalltalk, C++, Java, C#, Objective-C, Swift, JavaScript, and Python. In these and similar languages, one may call a method for division with syntax that resembles
where the parameters are optional. This is thought of as sending a message named divide with parameter divisor to dividend. An implementation will be chosen based only on dividend's type (perhaps rational, floating point, matrix), disregarding the type or value of divisor.
By contrast, some languages dispatch methods or functions based on the combination of operands; in the division case, the types of the dividend and divisor together determine which divide operation will be performed. This is known as multiple dispatch. Examples of languages that support multiple dispatch are Common Lisp, Dylan, and Julia.
A language may be implemented with different dynamic dispatch mechanisms. The choices of the dynamic dispatch mechanism offered by a language to a large extent alter the programming paradigms that are available or are most natural to use within a given language.