In
computer programming
Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of proc ...
, a generic function is a function defined for
polymorphism.
In statically typed languages
In statically typed languages (such as
C++ and
Java
Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...
), the term ''generic functions'' refers to a mechanism for ''compile-time polymorphism'' (
static dispatch), specifically
parametric polymorphism
In programming languages and type theory, parametric polymorphism allows a single piece of code to be given a "generic" type, using variables in place of actual types, and then instantiated with particular types as needed. Parametrically polymorph ...
. These are functions defined with
TypeParameters, intended to be resolved with
compile time
In computer science, compile time (or compile-time) describes the time window during which a language's statements are converted into binary instructions for the processor to execute. The term is used as an adjective to describe concepts relat ...
type information. The compiler uses these types to instantiate suitable versions, resolving any
function overloading
In some programming languages, function overloading or method overloading is the ability to create multiple functions of the same name with different implementations. Calls to an overloaded function will run a specific implementation of that f ...
appropriately.
In Common Lisp Object System
In some systems for
object-oriented programming
Object-oriented programming (OOP) is a programming paradigm based on the concept of '' objects''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impl ...
such as the
Common Lisp Object System
The Common Lisp Object System (CLOS) is the facility for object-oriented programming in American National Standards Institute, ANSI Common Lisp. CLOS is a powerful dynamic programming language, dynamic object system which differs radically from t ...
(CLOS) and
Dylan, a ''generic function'' is an entity made up of all methods having the same name. Typically a ''generic function'' is an instance of a class that
inherits both from ''function'' and ''standard-object''. Thus generic functions are both functions (that can be called with and applied to arguments) and ordinary objects. The book ''
The Art of the Metaobject Protocol'' explains the implementation and use of CLOS generic functions in detail.
One of the early object-oriented programming extensions to Lisp is
Flavors
Flavour or flavor is either the sensory perception of taste or smell, or a flavoring in food that produces such perception.
Flavour or flavor may also refer to:
Science
* Flavors (programming language), an early object-oriented extension to L ...
. It used the usual message sending paradigm influenced by
Smalltalk
Smalltalk is a purely object oriented programming language (OOP) that was originally created in the 1970s for educational use, specifically for constructionist learning, but later found use in business. It was created at Xerox PARC by Learni ...
. The Flavors syntax to send a message is:
(send object :message)
With New Flavors, it was decided the message should be a real function and the usual function calling syntax should be used:
(message object)
''message'' now is a ''generic function'', an object and function in its own right. Individual implementations of the ''message'' are called ''methods''.
The same idea was implemented in
CommonLoops.
New Flavors and CommonLoops were the main influence for the Common Lisp Object System.
Example
Common Lisp
Define a generic function with two parameters object-1 and object-2. The name of the generic function is ''collide''.
(defgeneric collide (object-1 object-2))
Methods belonging to the generic function are defined outside of classes.
Here we define a method for the generic function ''collide'' which is specialized for the classes asteroid (first parameter object-1) and spaceship (second parameter object-2). The parameters are used as normal variables inside the method body. There is no special namespace that has access to class slots.
(defmethod collide ((object-1 asteroid) (object-2 spaceship))
(format t "asteroid ~a collides with spaceship ~a" object-1 object-2))
Calling the generic function:
? (collide (make-instance 'asteroid) (make-instance 'spaceship))
asteroid # collides with spaceship #
Common Lisp can also retrieve individual methods from the generic function. FIND-METHOD finds the method from the generic function ''collide'' specialized for the classes ''asteroid'' and ''spaceship''.
? (find-method #'collide nil (list (find-class 'asteroid) (find-class 'spaceship)))
#
Comparison to other languages
Generic functions correspond roughly to what
Smalltalk
Smalltalk is a purely object oriented programming language (OOP) that was originally created in the 1970s for educational use, specifically for constructionist learning, but later found use in business. It was created at Xerox PARC by Learni ...
terms
methods, with the notable exception that, in Smalltalk, the receiver's class is the sole determinant of which body of code is called: the types or values of the arguments are irrelevant (
single 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 ...
). In a programming language with
multiple dispatch
Multiple dispatch or multimethods is a feature of some programming languages in which a Subroutine, function or Method (computer programming), method can be dynamic dispatch, dynamically dispatched based on the run time (program lifecycle phase), ...
when a generic function is called, method dispatch occurs on the basis of all arguments, not just one which is privileged.
New Flavors also provided generic functions, but only single dispatch.
In JavaScript, a generic function is a function that can work with values of different types, rather than a specific type. This is achieved through the use of type parameters or by dynamically checking the type of the value being operated on. One common use case for generic functions in JavaScript is to create reusable functions that can work with different data types, such as arrays, strings, or objects. JavaScript's dynamic typing system makes it particularly suited for the creation of generic functions, as values can be easily coerced or converted to different types as needed.
References
{{DEFAULTSORT:Generic Function
Method (computer programming)