Editing Generator (computer programming) (section)

{{Short description|Routine that generates a sequence of values}}
{{other uses|Generator (disambiguation)#Computing}}

{{Refimprove|date=July 2007}}

In [[computer science]], a '''generator''' is a [[subroutine|routine]] that can be used to control the [[iteration]] behaviour of a [[control flow#Loops|loop]]. All generators are also [[iterator]]s.<ref>[https://stackoverflow.com/q/1022564 What is the difference between an Iterator and a Generator?]</ref> A generator is very similar to a [[Function (computer programming)|function]] that returns an [[Array (data structure)|array]], in that a generator has [[Parameter (computer programming)|parameters]], can be called, and generates a sequence of values. However, instead of building an array containing all the values and returning them all at once, a generator ''yields'' the values one at a time, which requires less [[Computer memory|memory]] and allows the caller to get started processing the first few values immediately. In short, a generator ''looks like'' a function but ''behaves like'' an [[iterator]].

Generators can be implemented in terms of more expressive [[control flow]] constructs, such as [[coroutine]]s or first-class [[continuation]]s.<ref>{{cite web
| last = Kiselyov
| first = Oleg
|date=January 2004
| title = General ways to traverse collections in Scheme
| url = http://okmij.org/ftp/Scheme/enumerators-callcc.html
}}</ref> Generators, also known as semicoroutines,<ref name="Ralston2000">{{cite book|author=Anthony Ralston|title=Encyclopedia of computer science|url=https://books.google.com/books?id=yQ9LAQAAIAAJ|access-date=11 May 2013|year=2000|publisher=Nature Pub. Group|isbn=978-1-56159-248-7}}</ref> are a special case of (and weaker than) coroutines, in that they always yield control back to the caller (when passing a value back), rather than specifying a coroutine to jump to; see [[Coroutine#Generators|comparison of coroutines with generators]].