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In computing, static dispatch is a form of polymorphism fully resolved during compile time. It is a form of method dispatch, which describes how a language or environment will select which implementation of a method or function to use.
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 technique was formalized in 1989 as "F-bounded quantification."[2] The name "CRTP" was independently coined by Jim Coplien in 1995, [3] who had observed it in some of the earliest C++ template code as well as in code examples that Timothy Budd created in his multiparadigm language Leda. [4]
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.
Multiple dispatch should be distinguished from function overloading, in which static typing information, such as a term's declared or inferred type (or base type in a language with subtyping) is used to determine which of several possibilities will be used at a given call site, and that determination is made at compile or link time (or some ...
The C++ standards do not mandate exactly how dynamic dispatch must be implemented, but compilers generally use minor variations on the same basic model. Typically, the compiler creates a separate virtual method table for each class.
In statically typed languages (such as C++ and Java), the term generic functions refers to a mechanism for compile-time polymorphism (static dispatch), specifically parametric polymorphism. These are functions defined with TypeParameters, intended to be resolved with compile time type information.
Now, the multiple dispatch occurs in the call issued from the body of the anonymous function, and so traverse is just a mapping function that distributes a function application over the elements of an object. Thus all traces of the Visitor Pattern disappear, except for the mapping function, in which there is no evidence of two objects being ...