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{{Short description|
{{for|"for all" in logic (∀)|Universal quantification}}
[[File:For-Loop-Mint-Programming-Language-Type-2.gif|thumb|{{mono|foreach}} loops are almost always used to iterate over items in a sequence of elements.]]
{{Loop constructs}}<!-- DO NOT remove. Discuss navigation concept at [[Talk:Do while loop#Helpbox experiment]] -->
In [[computer programming]], '''foreach loop''' (or '''for-each loop''') is a [[control flow]] statement for traversing items in a [[Collection class|collection]]. {{mono|foreach}} is usually used in place of a standard {{mono|[[For loop|for]]}} loop [[Statement (computer science)|statement]]. Unlike other {{mono|for}} loop constructs, however, {{mono|foreach}} loops<ref>{{cite web
| url=http://www.digitalmars.com/d/statement.html#ForeachStatement
| title=D Programming Language <
| access-date=2008-08-04
| publisher=Digital Mars
}}</ref> usually maintain no explicit counter: they essentially say "do this to everything in this set", rather than "do this
The
The
== Syntax ==
Syntax varies among languages. Most use the simple word <code>for</code>, although other use the more logical word <code>foreach</code>, roughly as follows:
}
== Language support ==
[[Programming language]]s which support foreach loops include [[ABC (programming language)|ABC]], [[ActionScript]], [[Ada (programming language)|Ada]], [[C++]] (since [[C++11]]), [[C Sharp (programming language)|C#]], [[ColdFusion Markup Language]] (CFML), [[Cobra (programming language)|Cobra]], [[D (programming language)|D]], [[Daplex]] (query language), [[Delphi (software)|Delphi]], [[ECMAScript]], [[Erlang (programming language)|Erlang]], [[Java (programming language)|Java]] (since 1.5), [[JavaScript]], [[Lua (programming language)|Lua]], [[Objective-C]] (since 2.0), [[ParaSail (programming language)|ParaSail]], [[Perl]], [[PHP]], [[Prolog]],<ref>{{Cite web |url=https://www.swi-prolog.org/pldoc/man?predicate=foreach/2 |title=SWI-Prolog – foreach/2 |website=Swi-prolog.org |access-date=2020-02-10}}</ref> [[Python (programming language)|Python]], [[R (programming language)|R]], [[REALbasic]], [[Rebol]],<ref>{{Cite web |url=http://www.rebol.com/ |title=Rebol}}</ref> [[Red (programming language)|Red]],<ref>{{Cite web |url=https://www.red-lang.org/ |title=Red Programming Language}}</ref> [[Ruby (programming language)|Ruby]], [[Scala (programming language)|Scala]], [[Smalltalk]], [[Swift (programming language)|Swift]], [[Tcl]], [[tcsh]], [[Unix shell]]s, [[Visual Basic (.NET)]], and [[Windows PowerShell]]. Notable languages without foreach are [[C (programming language)|C]], and C++ pre-C++11.
=== ActionScript 3.0 ===
[[ActionScript]] supports the ECMAScript 4.0 Standard<ref>{{cite web|url=https://www.ecma-international.org/activities/Languages/Language%20overview.pdf |title=Proposed ECMAScript 4th Edition – Language Overview |access-date=2020-02-21}}</ref> for <code>for each .. in</code><ref>{{cite web|url=https://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/statements.html#for_each..in |title=for each..in |access-date=2020-02-21}}</ref> which pulls the value at each index.
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=== Ada ===
{{Wikibooks|Ada Programming|Control}}
[[Ada (programming language)|Ada]] supports foreach loops as part of the normal [[for loop]]. Say X is an [[Array data structure|array]]:
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Most general: string or array as collection (collection size known at run-time)
: ''
<syntaxhighlight lang="c" highlight="5-8" line>
#include <stdio.h>
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=== C++ ===
[[C++11]] provides a foreach loop. The syntax is similar to that of [[Foreach loop#Java|Java]]:
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C++11 range-based for statements have been implemented in [[GNU Compiler Collection]] (GCC) (since version 4.6), [[Clang]] (since version 3.0) and [[Visual C++]] 2012 (version 11 <ref>{{cite web|url=http://blogs.msdn.com/b/vcblog/archive/2011/09/12/10209291.aspx |title=C++11 Features in Visual C++ 11 - Visual C++ Team Blog - Site Home - MSDN Blogs |publisher=Blogs.msdn.com |date=2011-09-12 |access-date=2013-08-04}}</ref>)
The range-based <
<syntaxhighlight lang="Cpp">
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</syntaxhighlight>
The compiler uses [[argument-dependent lookup]] to resolve the <
The [[C++ Standard Library]] also supports <
<syntaxhighlight lang="Cpp">
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std::vector<int> v {1, 2, 3, 4, 5};
std::for_each(v.begin(), v.end(), [
{
std::cout << i << '\n';
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std::cout << "reversed but skip 2 elements:\n";
std::for_each(v.rbegin()+2, v.rend(), [
{
std::cout << i << '\n';
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=== C++/CLI ===
The [[C++/CLI]] language proposes a construct similar to C#.
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<!-- At the time of writing, there is no documented C++/CLI support in the [[mw:Extension:SyntaxHighlight GeSHi|MediaWiki syntax highliter]] -->
<syntaxhighlight lang="c#">
{
}
</syntaxhighlight>
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==== Script syntax ====
<syntaxhighlight lang="cfs">
// arrays
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==== Tag syntax ====
<syntaxhighlight lang="CFM">
<!--- arrays --->
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=== Common Lisp ===
[[Common Lisp]] provides foreach ability either with the ''dolist'' macro:
<syntaxhighlight lang="LISP">
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=== D ===
{{Main|D (programming language)}}
<syntaxhighlight lang="D">
foreach(item; set) {
// do something to item
}
</syntaxhighlight>
or
<syntaxhighlight lang="D">
foreach(argument) {
// pass value
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=== Dart ===
{{Main|Dart (programming language)}}
<syntaxhighlight lang="Java">
for (final element in someCollection) {
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=== Object Pascal, Delphi ===
{{Main|Object Pascal|Delphi (software)}}
Foreach support was added in [[Delphi (software)|Delphi]] 2005, and uses an enumerator variable that must be declared in the ''var'' section.
<syntaxhighlight lang="Delphi">
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=== Eiffel ===
The iteration (foreach) form of the [[Eiffel (programming language)|Eiffel]] loop construct is introduced by the keyword <code lang=Eiffel>across</code>.
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=== Go ===
[[Go (programming language)|Go]]'s foreach loop can be used to loop over an array, slice, string, map, or channel.
Using the two-value form
<syntaxhighlight lang="go">
for index, value := range someCollection {
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</syntaxhighlight>
Using the one-value form
<syntaxhighlight lang="go">
for index := range someCollection {
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=== Groovy ===
[[Groovy (programming language)|Groovy]] supports ''for'' loops over collections like arrays, lists and ranges:
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Collections in Groovy can also be iterated over using the ''each'' keyword
and a closure.
<syntaxhighlight lang="Groovy">
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=== Haskell ===
[[Haskell]] allows looping over lists with [[Monad (functional programming)|monadic]] actions using <code>mapM_</code> and <code>forM_</code> (<code>mapM_</code> with its arguments flipped) from [http://hackage.haskell.org/package/base-4.6.0.1/docs/Control-Monad.html Control.Monad]:
{| class="wikitable"
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=== Java ===
In [[Java (programming language)|Java]], a foreach-construct was introduced in [[Java Development Kit]] (JDK) 1.5.0.<ref name="jdk5release">
"Enhanced for Loop - This new language construct[...]"
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|year=2004
|publisher=[[Sun Microsystems, Inc.]]
}}</ref><ref name=Bloch>{{cite book | title= "Effective Java: Programming Language Guide" |last=Bloch| first=Joshua| publisher=Addison-Wesley | edition=third | isbn=978-0134685991| year=2018}}</ref>{{rp|264}}
<syntaxhighlight lang="Java">
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// Do something to item
}
</syntaxhighlight>
Java also provides the stream api since java 8:<ref name=Bloch>{{cite book | title= "Effective Java: Programming Language Guide" |last=Bloch| first=Joshua| publisher=Addison-Wesley | edition=third | isbn=978-0134685991| year=2018}}</ref>{{rp|294-203}}
<syntaxhighlight lang="Java">
List<Integer> intList = List.of(1, 2, 3, 4);
intList.stream().forEach(i -> System.out.println(i));
</syntaxhighlight>
=== JavaScript ===
The [[
<syntaxhighlight lang="JavaScript">
for (var item of array){
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</syntaxhighlight>
Alternatively, function-based style: <ref>
<syntaxhighlight lang="JavaScript">
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</syntaxhighlight>
To limit the iteration to the object's own properties, excluding those inherited through the prototype chain, it is sometimes useful to add a hasOwnProperty() test,
<syntaxhighlight lang="JavaScript">
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</syntaxhighlight>
=== Lua ===
{{Main|Lua (programming language)}}
Source:<ref>{{Cite web|url=https://en.wikibooks.org/wiki/Lua_Programming/Tables#Foreach_loop|title=Lua Programming/Tables - Wikibooks, open books for an open world|website=en.wikibooks.org|language=en|access-date=2017-12-06}}</ref>
Iterate only through numerical index values:<syntaxhighlight lang="lua">
for index, value in ipairs(array) do
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=== Mathematica ===
In [[Mathematica]], <code>Do</code> will simply evaluate an expression for each element of a list, without returning any value.
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=== MATLAB ===
{{Main|MATLAB}}
<syntaxhighlight lang="MATLAB">
for item = array
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=== Mint ===
For each loops are supported in Mint, possessing the following syntax:
<syntaxhighlight lang="Ruby">
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=== Objective-C ===
Foreach loops, called [[Objective-C#Fast enumeration|Fast enumeration]], are supported starting in [[Objective-C]] 2.0. They can be used to iterate over any object that implements the NSFastEnumeration protocol, including NSArray, NSDictionary (iterates over keys), NSSet, etc.
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NSArray *a = [NSArray new]; // Any container class can be substituted
for(id obj in a) { //
//
//
printf("%s\n", [[obj description] UTF8String]); // Must use UTF8String with %s
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=== OCaml ===
[[OCaml]] is a [[functional programming]] language. Thus, the equivalent of a foreach loop can be achieved as a library function over lists and arrays.
For lists:
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=== ParaSail ===
The [[ParaSail (programming language)|ParaSail]] parallel programming language supports several kinds of iterators, including a general "for each" iterator over a container:
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=== Pascal ===
In [[Pascal (programming language)|Pascal]], ISO standard 10206:1990 introduced iteration over [[Pascal (programming language)#Set types|set types]], thus:
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=== Perl ===
In [[Perl]], ''foreach'' (which is equivalent to the shorter for) can be used to traverse elements of a list. The expression which denotes the collection to loop over is evaluated in list-context and each item of the resulting list is, in turn, aliased to the loop variable.
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=== PHP ===
{{Main|
<syntaxhighlight lang="php">
foreach ($set as $value) {
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<syntaxhighlight lang="php">
$arr = array(1, 2, 3);
foreach ($arr as &$value) { //
$value++;
}
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=== Python ===
{{Main|Python (programming language)}}
<syntaxhighlight lang="python">
for item in iterable_collection:
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# Do stuff with item
# Possibly assign it back to seq[i]
</syntaxhighlight>
=== R ===
{{Main|R (programming language)}}
<syntaxhighlight lang="R">
for (item in object) {
# Do something with item
}
</syntaxhighlight>
As <code>for ... in</code> is the only kind of <code>for</code> loop in R, the equivalent to the "counter" loop found in other languages is...
<syntaxhighlight lang="R">
for (i in seq_along(object)) {
# Do something with object[[i]]
}
</syntaxhighlight>
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=== Raku ===
In [[Raku (programming language)|Raku]], a sister language to Perl, ''for'' must be used to traverse elements of a list (''foreach'' is not allowed). The expression which denotes the collection to loop over is evaluated in list-context, but not flattened by default, and each item of the resulting list is, in turn, aliased to the loop variable(s).
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=== Ruby ===
{{Main|Ruby (programming language)}}
<syntaxhighlight lang="Ruby">
set.each do |item|
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<syntaxhighlight lang="Ruby">
set.each do |
# do something to
# do something to value
end
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=== Rust ===
{{Main|Rust (programming language)}}
The <code>for</code> loop has the structure <syntaxhighlight lang="rust" inline>for <pattern> in <expression> { /* optional statements */ }</syntaxhighlight>. It implicitly calls the [https://doc.rust-lang.org/std/iter/trait.IntoIterator.html <code>IntoIterator::into_iter</code>] method on the expression, and uses the resulting value, which must implement the [https://doc.rust-lang.org/std/iter/trait.Iterator.html <code>Iterator</code>] trait. If the expression is itself an iterator, it is used directly by the <code>for</code> loop through an [https://doc.rust-lang.org/std/iter/trait.IntoIterator.html#impl-IntoIterator-25 implementation of <code>IntoIterator</code> for all <code>Iterator</code>s] that returns the iterator unchanged. The loop calls the <code>Iterator::next</code> method on the iterator before executing the loop body. If <code>Iterator::next</code> returns <code>[[option type|Some(_)]]</code>, the value inside is assigned to the [[pattern matching|pattern]] and the loop body is executed; if it returns <code>None</code>, the loop is terminated.
<syntaxhighlight lang="Rust">
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=== Scala ===
{{Main|Scala (programming language)}}
<syntaxhighlight lang="Scala">
// return list of modified elements
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=== Swift ===
[[Swift (programming language)|Swift]] uses the <code>for</code>…<code>in</code> construct to iterate over members of a collection.<ref>{{Cite web|url=https://developer.apple.com/library/prerelease/ios/documentation/swift/conceptual/swift_programming_language/ControlFlow.html#//apple_ref/doc/uid/TP40014097-CH9-XID_153|title=Control Flow — the Swift Programming Language (Swift 5.5)}}</ref>
<syntaxhighlight lang="objc">
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=== SystemVerilog ===
[[SystemVerilog]] supports iteration over any vector or array type of any dimensionality using the <code>foreach</code> keyword.
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=== Tcl ===
[[Tcl]] uses foreach to iterate over lists. It is possible to specify more than one iterator variable, in which case they are assigned sequential values from the list.
{| class="wikitable"
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|}
=== Visual Basic (.NET) ===
{{Main|Visual Basic (.NET)}}
<syntaxhighlight lang="VBNet">
For Each item In enumerable
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</syntaxhighlight>
or without [[type inference]]
<syntaxhighlight lang="VBNet">
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</syntaxhighlight>
===
{{Main|XSLT}}
<syntaxhighlight lang="xml">
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{{Reflist|2}}
[[Category:Control flow]]
[[Category:Iteration in programming]]
[[Category:Programming language comparisons]]
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