Editing Callback (computer programming) (section)

== Implementation ==

The callback technology is implemented differently by [[programming language]].

In [[Assembly language|assembly]], [[C (programming language)|C]], [[C++]], [[Pascal (programming language)|Pascal]], [[Modula2]] and other languages, a callback function is stored internally as a [[function pointer]]. Using the same storage allows different languages to directly share callbacks without a [[program lifecycle phase|design-time or runtime]] [[interoperability]] [[Abstraction layer|layer]]. For example, the [[Windows API]] is accessible via multiple languages, compilers and assemblers.

C++ also allows objects to provide an implementation of the function call operation. The [[Standard Template Library]] accepts these objects (called ''[[function object|functors]]'') as parameters.

Many [[Dynamic programming language|dynamic languages]], such as [[JavaScript]], [[Lua (programming language)|Lua]], [[Python (programming language)|Python]], [[Perl]]<ref>{{cite web |url=http://www.unix.org.ua/orelly/perl/cookbook/ch11_05.htm |title=Perl Cookbook - 11.4. Taking References to Functions|date=2 July 1999 |accessdate=2008-03-03}}</ref><ref>{{cite web |url=http://www.unix.org.ua/orelly/perl/advprog/ch04_02.htm |title=Advanced Perl Programming - 4.2 Using Subroutine References |date=2 July 1999 |accessdate=2008-03-03}}</ref> and [[PHP]], allow a function object to be passed.

[[List of CLI languages|CLI languages]] such as [[C Sharp (programming language)|C#]] and [[VB.NET]] provide a [[type safety|type-safe]] encapsulating function reference known as [[Delegate (CLI)|delegate]].

Events and [[event handlers]], as used in .NET languages, provide for callbacks.

Functional languages generally support [[first-class functions]], which can be passed as callbacks to other functions, stored as data or returned from functions.

Many languages, including Perl, Python, [[Ruby (programming language)|Ruby]], [[Smalltalk]], [[C++]] (11+), C# and VB.NET (new versions) and most functional languages, support [[lambda (programming)|lambda expressions]], unnamed functions with inline syntax, that generally acts as callbacks..

In some languages, including [[Scheme (programming language)|Scheme]], [[ML (programming language)|ML]], JavaScript, Perl, Python, Smalltalk, PHP (since 5.3.0),<ref>{{cite web |url=https://secure.php.net/manual/en/functions.anonymous.php |title=PHP Language Reference - Anonymous functions | accessdate=2011-06-08}}</ref> C++ (11+), Java (since 8),<ref>{{cite web |url=http://www.oracle.com/technetwork/java/javase/8-whats-new-2157071.html|title=What's New in JDK 8|work=oracle.com}}</ref> and many others, a lambda can be a [[Closure (computer science)|closure]], i.e. can access variables locally defined in the context in which the lambda is defined.

In an [[object-oriented programming]] language such as [[Java (programming language)|Java]] versions before function-valued arguments, the behavior of a callback can be achieved by passing an object that implements an interface. The methods of this object are callbacks.

In [[PL/I]] and [[ALGOL 60]] a callback procedure may need to be able to access local variables in containing blocks, so it is called through an ''entry variable'' containing both the entry point and context information. <ref>{{cite book |editor1-last=Belzer |editor1-first=Jack |editor2-last=Holzman |editor2-first=Albert G |editor3-last=Kent |editor3-first=Allen |title=Encyclopedia of Computer Science and Technology: Volume 12 |date=1979 |publisher=Marcel Dekker, inc. |isbn=0-8247-2262-0 |page=164 |url=https://books.google.com/books?id=IFmaqTI9-KsC&pg=PA164 |access-date=January 28, 2024}}</ref>