Editing First-class citizen (section)

==Examples==

The simplest [[Scalar (computing)|scalar]] data types, such as integer and floating-point numbers, are nearly always first-class.

In many older languages, [[array data type|arrays]] and strings are not first-class: they cannot be assigned as objects or passed as parameters to a subroutine. For example, neither [[Fortran IV]] nor [[C (programming language)|C]] supports array assignment, and when they are passed as parameters, only the position of their first element is actually passed—their size is lost. C appears to support assignment of array [[pointer (computing)|pointers]], but in fact these are simply pointers to the array's first element, and again do not carry the array's size.{{citation needed|date=January 2022}}

In most languages, [[data types]] are not first-class objects, though in some object-oriented languages, [[Class (computer programming)|classes]] are first-class objects and are instances of [[metaclass]]es. Languages in the [[functional programming]] family often also feature first-class types, in the form of, for example, [[generalized algebraic data type]]s, or other metalanguage amenities enabling programs to implement extensions to their own implementation language.

Few languages support [[continuation]]s and [[GOTO]]-labels as objects at all, let alone as first-class objects.

{| class=wikitable
! Concept !! Description !! Languages
|-
| [[first-class function]] || [[closure (computer science)|closure]]s and [[anonymous function]]s || [[Smalltalk]], [[Dart (programming language)|Dart]], [[Scheme (programming language)|Scheme]], [[ML (programming language)|ML]], [[Haskell (programming language)|Haskell]], [[F Sharp (programming language)|F#]], [[Kotlin (programming language)|Kotlin]], [[Scala (programming language)|Scala]], [[Swift (programming language)|Swift]], [[Perl]], [[PHP]], [[Python (programming language)|Python]], [[Raku (programming language)|Raku]], [[JavaScript]], [[Delphi (programming language)|Delphi]], [[Rust (programming language)|Rust]], [[Common Lisp#Functions|Common Lisp]]
|-
| [[first-class control]] || [[continuation]]s || [[Scheme (programming language)|Scheme]], [[ML (programming language)|ML]], [[F Sharp (programming language)|F#]]
|-
| [[first-class type]] || [[dependent types]] || [[Coq (software)|Coq]], [[Idris (programming language)|Idris]], [[Agda (programming language)|Agda]]
|-
| [[first-class data type]] || || [[Generic Haskell]], C++11
|-
| [[first-class polymorphism]] || [[impredicative polymorphism]] || 
|-
| [[first-class message]] || dynamic [[message (object-oriented programming)|message]]s (method calls) || [[Smalltalk]],<ref name="shroff-smith">Paritosh Shroff, Scott F. Smith. ''[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.114.4468&rep=rep1&type=pdf Type Inference for First-Class Messages with Match-Functions]''</ref> [[Objective-C]],<ref name="shroff-smith" /> [[Generic_function#In_Common_Lisp_Object_System|Common Lisp]]
|-
| [[first-class class]] || [[metaclass]] and [[metaobject]] || [[Smalltalk]], [[Objective-C]], [[Ruby (programming language)|Ruby]], [[Python (programming language)|Python]], [[Delphi (programming language)|Delphi]], [[Common Lisp#Common_Lisp_Object_System_(CLOS)|Common Lisp]]
|-
| first-class proofs <!-- proofs are first-class in IIT according to "Dependent Types at Work" --> || [[proof object]]<ref>{{cite book|last2=Dybjer|first2=Peter|date=2009|chapter=Dependent Types at Work|chapter-url=http://www.cse.chalmers.se/~peterd/papers/DependentTypesAtWork.pdf|title=Language Engineering and Rigorous Software Development|volume=5520|pages=57–99|doi=10.1007/978-3-642-03153-3_2|last1=Bove|first1=Ana|series=Lecture Notes in Computer Science |isbn=978-3-642-03152-6 |access-date=8 June 2015|url-status=live|archive-url=https://web.archive.org/web/20140402095457/http://www.cse.chalmers.se/~peterd/papers/DependentTypesAtWork.pdf|archive-date=April 2, 2014}} <!-- add back if original becomes obsolete | archiveurl = https://web.archive.org/web/20140402095457/http://www.cse.chalmers.se/~peterd/papers/DependentTypesAtWork.pdf | archivedate = 2014-04-02}} --> (also [http://www.cse.chalmers.se/~peterd/papers/DependentTypesAtWork.pdf archived])</ref> || [[Coq (software)|Coq]], [[Agda (programming language)|Agda]]
|}