Editing At sign (section)

=== Computer languages ===
@ is used in various [[programming language]]s and other [[computer language]]s, although there is not a consistent theme to its usage. For example:
* In [[ActionScript]], @ is used in XML parsing and traversal as a string prefix to identify attributes in contrast to child elements.<ref>{{Cite web |title=Operators – Adobe ActionScript® 3 (AS3) API Reference |url=https://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/operators.html#attribute_identifier |access-date=2023-05-12 |website=help.adobe.com |language=en-us |archive-date=2023-05-12 |archive-url=https://web.archive.org/web/20230512112456/https://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/operators.html#attribute_identifier |url-status=live }}</ref>
* In [[Ada (programming language)|Ada]] 2022, @ is the ''target name'' symbol, an abbreviation of the [[Sides of an equation|LHS]] of an assignment; it is used to avoid repetition of potentially long names in assignment statements.<ref>{{Cite web |url=http://www.ada-auth.org/standards/22rm/html/rm-5-2-1.html |title=Ada Reference Manual (Ada 2022). Target Name Symbols |website=ada-auth.org |access-date=2024-07-16}}</ref> For example: <code>A_Very_Long_Variable_Name := A_Very_Long_Variable_Name + 1;</code> is shortened to <code>A_Very_Long_Variable_Name := @ + 1;</code>, increasing readability.
* In [[ALGOL 68]], the @ symbol is ''brief form'' of the '''at''' [[keyword (computer programming)|keyword]]; it is used to change the lower bound of an array. For example: {{code|arrayx[@88]}} refers to an array starting at index 88.<ref>{{Cite journal |last=van Wijngaarden |first=A. |date=1981-08-16 |title=Revised Report of the Algorithmic Language Algol 68 |url=https://dl.acm.org/doi/10.5555/1064084.1064085 |journal=ALGOL Bulletin |issue=Sup 47 |pages=121, 532 |doi= |issn=0084-6198 |access-date=2023-05-12 |archive-date=2023-05-12 |archive-url=https://web.archive.org/web/20230512112455/https://dl.acm.org/doi/10.5555/1064084.1064085 |url-status=live }}</ref>
* In Dyalog [[APL (programming language)|APL]], @ is used as a functional way to modify or replace data '''at''' specific locations in an array.
* In the [[ASP.NET MVC]] [[Microsoft ASP.NET Razor view engine|Razor]] template markup syntax, the @ character denotes the start of code statement blocks or the start of text content.<ref>{{Cite web |last=Phil Haack |title=Razor syntax quick reference |date=6 January 2011 |url=http://haacked.com/archive/2011/01/06/razor-syntax-quick-reference.aspx |access-date=12 January 2013 |archive-date=26 January 2022 |archive-url=https://web.archive.org/web/20220126032007/http://haacked.com/archive/2011/01/06/razor-syntax-quick-reference.aspx/ |url-status=live }}</ref><ref>{{Cite web |title=ASP.NET MVC 3: Razor's @: and &lt;text&gt; syntax |url=https://weblogs.asp.net/scottgu/asp-net-mvc-3-razor-s-and-lt-text-gt-syntax |access-date=2020-04-30 |website=weblogs.asp.net |date=16 December 2010 |language=en-US |archive-date=2020-07-26 |archive-url=https://web.archive.org/web/20200726111727/https://weblogs.asp.net/scottgu/asp-net-mvc-3-razor-s-and-lt-text-gt-syntax |url-status=live }}</ref>
* In [[Assembly language]], @ is sometimes used as a [[dereference operator]].<ref>{{Cite web |title=assembly – @ sign in assembler? – Stack Overflow |url=https://stackoverflow.com/questions/11214675/sign-in-assembler |website=stackoverflow.com |access-date=2021-05-02 |archive-date=2021-10-05 |archive-url=https://web.archive.org/web/20211005220705/https://stackoverflow.com/questions/11214675/sign-in-assembler |url-status=live }}</ref>
* In [[CSS]], @ is used in special statements outside of a CSS block.<ref>{{Cite web |title=At-rules |url=https://developer.mozilla.org/en-US/docs/Web/CSS/At-rule |access-date=2020-04-30 |website=MDN Web Docs |language=en |archive-date=2020-05-05 |archive-url=https://web.archive.org/web/20200505194617/https://developer.mozilla.org/en-US/docs/Web/CSS/At-rule |url-status=live }}</ref>
* In [[C Sharp (programming language)|C#]], it denotes "verbatim strings", where no characters are escaped and two double-quote characters represent a single double-quote.<ref>[http://msdn.microsoft.com/en-us/library/aa691090%28v=vs.71%29.aspx 2.4.4.5 String literals] {{Webarchive|url=https://web.archive.org/web/20120805045534/http://msdn.microsoft.com/en-us/library/aa691090(v=vs.71).aspx |date=2012-08-05 }},</ref> As a prefix it also allows keywords to be used as [[identifier (computer programming)|identifiers]],<ref>{{Cite web |title=2.4.2 Identifiers |url=http://msdn.microsoft.com/en-us/library/aa664670%28v=vs.71%29.aspx |access-date=2012-08-16 |archive-date=2012-08-10 |archive-url=https://web.archive.org/web/20120810204003/http://msdn.microsoft.com/en-us/library/aa664670(v=vs.71).aspx |url-status=live }}</ref> a form of [[Stropping (syntax)|stropping]].
* In [[D (programming language)|D]], it denotes function attributes: like: <code>@safe</code>, <code>@nogc</code>, user defined <code>@('from_user')</code> which can be evaluated at compile time (with <code>__traits</code>) or <code>@property</code> to declare properties, which are functions that can be syntactically treated as if they were fields or variables.<ref>{{Cite web |title=Attributes – D Programming Language |url=https://dlang.org/spec/attribute.html |website=dlang.org |access-date=2018-06-22 |archive-date=2018-12-08 |archive-url=https://web.archive.org/web/20181208115642/https://dlang.org/spec/attribute.html |url-status=live }}</ref>
* In [[DIGITAL Command Language]], the @ character was the command used to execute a command procedure. To run the command procedure VMSINSTAL.COM, one would type <code>@VMSINSTAL</code> at the command prompt.
* In the [[Domain Name System]] (DNS), @ is used to represent the {{code|$ORIGIN}}, typically the "root" of the domain without a prefixed sub-domain. (Ex: wikipedia.org vs. www.wikipedia.org)
* In [[Forth (programming language)|Forth]], it is used to fetch values from the address on the top of the stack. The operator is pronounced as "fetch".
* In [[Haskell]], it is used in so-called ''as-patterns''. This notation can be used to give aliases to [[pattern matching|patterns]], making them more readable.
* in [[HTML]], it can be encoded as <code>&amp;commat;</code><ref>{{cite web |url=https://dev.w3.org/html5/html-author/charref |title=Character Entity Reference Chart |date= |website=[[World Wide Web Consortium]] (W3C) |access-date=2022-02-08 |archive-date=2021-02-27 |archive-url=https://web.archive.org/web/20210227130216/https://dev.w3.org/html5/html-author/charref |url-status=live }}</ref>
* In [[J (programming language)|J]], denotes [[function composition]].
* In [[Java (programming language)|Java]], it has been used to denote [[Java annotation|annotations]], a kind of metadata, since version 5.0.<ref>{{Cite web |title=in java what does the @ symbol mean? |url=https://stackoverflow.com/questions/31822020/in-java-what-does-the-symbol-mean |access-date=2020-04-30 |website=Stack Overflow |archive-date=2020-07-26 |archive-url=https://web.archive.org/web/20200726125845/https://stackoverflow.com/questions/31822020/in-java-what-does-the-symbol-mean |url-status=live }}</ref>
* In [[Julia (programming language)|Julia]], it denotes the invocation of a macro.<ref>{{cite web |title=Metaprogramming · The Julia Language |url=https://docs.julialang.org/en/v1/manual/metaprogramming/#man-macros |website=docs.julialang.org |access-date=2023-08-23 |archive-date=2023-06-23 |archive-url=https://web.archive.org/web/20230623204719/https://docs.julialang.org/en/v1/manual/metaprogramming/ |url-status=live }}</ref>
* In [[LiveCode]], it is prefixed to a parameter to indicate that the parameter is [[Pass by reference|passed by reference]].
* In an [[LXDE]] autostart file (as used, for example, on the [[Raspberry Pi]] computer), @ is prefixed to a command to indicate that the command should be automatically re-executed if it crashes.<ref>{{Cite web |title=LXSession - LXDE.org |url=https://wiki.lxde.org/en/LXSession#Settings |access-date=2020-04-30 |website=wiki.lxde.org |archive-date=2020-07-14 |archive-url=https://web.archive.org/web/20200714075921/https://wiki.lxde.org/en/LXSession#Settings |url-status=live }}</ref>
* In a [[Makefile]], @ specifies to not output the command before it is executed.
* In [[ML (programming language)|ML]], it denotes list concatenation.
* In [[modal logic]], specifically when representing [[possible world]]s, @ is sometimes used as a logical symbol to denote the actual world (the world we are "at").
* In [[Objective-C]], @ is prefixed to language-specific keywords such as @implementation and to form string literals.
* In InterSystems [[Caché ObjectScript|ObjectScript]], @ is the indirection operator, enabling dynamic runtime substitution of part or all of a command line, a command, or a command argument.<ref>{{Cite web |title=Indirection – InterSystems IRIS Documentation|url=https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls?KEY=RCOS_op_indirection|access-date=2025-01-31|website=docs.intersystems.com|language=en-us|url-status=live}}</ref>
* In [[Pascal (programming language)|Pascal]], @ is the "address of" operator (it tells the location at which a variable is found).
* In [[Perl]], @ prefixes [[Variable (programming)|variables]] which contain [[Array data structure|arrays]] {{code|@array}}, including array [[Array slicing#1987: Perl|slices]] {{code|@array[2..5,7,9]}} and [[Hash table#Associative arrays|hash]] slices {{code|@hash{'foo', 'bar', 'baz'}|perl}} or {{code|@hash{qw(foo bar baz)}|perl}}. This use is known as a ''[[Sigil (computer programming)|sigil]]''.
* In [[PHP]], it is used just before an [[Expression (programming)|expression]] to make the [[Interpreter (computing)|interpreter]] suppress errors that would be generated from that expression.<ref>{{Cite web |title=PHP: Error Control Operators – Manual |url=https://www.php.net/manual/en/language.operators.errorcontrol.php |access-date=2020-04-30 |website=www.php.net |archive-date=2020-05-08 |archive-url=https://web.archive.org/web/20200508094533/https://www.php.net/manual/en/language.operators.errorcontrol.php |url-status=live }}</ref>
* In [[Python (programming language)|Python]] 2.4 and up, it is used to [[Python syntax and semantics#Decorators|decorate a function]] (wrap the function in another one at creation time). In Python 3.5 and up, it is also used as an [[Overload (programming)|overloadable]] [[matrix multiplication]] operator.<ref>{{Cite web |title=syntax – What does the "at" (@) symbol do in Python? |url=https://stackoverflow.com/questions/6392739/what-does-the-at-symbol-do-in-python |access-date=2020-04-30 |website=Stack Overflow |archive-date=2020-04-24 |archive-url=https://web.archive.org/web/20200424180918/https://stackoverflow.com/questions/6392739/what-does-the-at-symbol-do-in-python |url-status=live }}</ref>
*In [[R (programming language)|R]] and [[S-PLUS]], it is used to extract slots from S4 objects.<ref>{{Cite web |title= The S4 object system |url=http://adv-r.had.co.nz/S4.html |access-date=2023-08-18 |website=adv-r.had.co.nz/ |archive-date=2022-12-06 |archive-url=https://web.archive.org/web/20221206085835/http://adv-r.had.co.nz/S4.html |url-status=live }}</ref>
*In [[ASP.NET Razor|Razor]], it is used for [[C Sharp (programming language)|C#]] code blocks.<ref>{{Cite web |title=Usage of the @ (at) sign in ASP.NET |url=https://www.mikesdotnetting.com/article/258/usage-of-the-at-sign-in-asp-net |access-date=2020-04-30 |website=www.mikesdotnetting.com |archive-date=2020-04-04 |archive-url=https://web.archive.org/web/20200404105645/http://www.mikesdotnetting.com/article/258/usage-of-the-at-sign-in-asp-net |url-status=live }}</ref>
* In [[Ruby (programming language)|Ruby]], it functions as a sigil: <code>@</code> prefixes [[instance variable]]s, and <code>@@</code> prefixes [[class variable]]s.<ref>{{Cite web |title=syntax – What does @@variable mean in Ruby? |url=https://stackoverflow.com/questions/5890118/what-does-variable-mean-in-ruby |access-date=2020-05-05 |website=Stack Overflow |archive-date=2020-07-26 |archive-url=https://web.archive.org/web/20200726105629/https://stackoverflow.com/questions/5890118/what-does-variable-mean-in-ruby |url-status=live }}</ref>
* In [[Rust (programming language)|Rust]], it is used to bind values matched by a pattern to a variable.<ref>{{cite web |title=Patterns |url=https://doc.rust-lang.org/reference/patterns.html#identifier-patterns |website=The Rust Reference |access-date=21 July 2023 |archive-url=https://web.archive.org/web/20230618030139/https://doc.rust-lang.org/reference/patterns.html#identifier-patterns |archive-date=18 June 2023 |url-status=live}}</ref>
* In [[Scala (programming language)|Scala]], it is used to denote annotations (as in Java), and also to bind names to subpatterns in pattern-matching expressions.<ref>{{Cite web |title=Scala @ operator |url=https://stackoverflow.com/questions/2359014/scala-operator |access-date=2020-05-05 |website=Stack Overflow |archive-date=2020-07-26 |archive-url=https://web.archive.org/web/20200726112338/https://stackoverflow.com/questions/2359014/scala-operator |url-status=live }}</ref>
* In [[Swift (programming language)|Swift]], <code>@</code> prefixes "annotations" that can be applied to classes or members. Annotations tell the compiler to apply special semantics to the declaration like keywords, without adding keywords to the language.
* In [[T-SQL]], <code>@</code> prefixes variables and <code>@@</code> prefixes "niladic" system functions.
* In several [[xBase]]-type programming languages, like [[DBASE]], [[FoxPro]]/[[Visual FoxPro]] and [[Clipper (programming language)|Clipper]], it is used to denote position on the screen. For example: {{code|@1,1 SAY "HELLO"|xbase}} to show the word "HELLO" in line 1, column 1.
** In FoxPro/Visual FoxPro, it is also used to indicate explicit [[pass by reference]] of variables when calling [[Subroutine|procedures or functions]] (but it is not an [[Memory address|address]] [[Operator (programming)|operator]]).<ref>{{Cite web |title=Visual FoxPro Programming Language Online Help: SET UDFPARMS (Command), or MSDN Library 'How to: Pass Data to Parameters by Reference'. |date=18 June 2008 |url=http://msdn.microsoft.com/en-us/library/z9b11381.aspx |access-date=2011-02-19 |publisher=Microsoft, Inc. |archive-date=2012-10-22 |archive-url=https://web.archive.org/web/20121022193155/http://msdn.microsoft.com/en-us/library/z9b11381.aspx |url-status=live }}</ref>
* In a Windows [[Batch file]], an <code>@</code> at the start of a line suppresses the [[Echo (command)|echoing]] of that command. In other words, is the same as <code>ECHO OFF</code> applied to the current line only. Normally a Windows command is executed and takes effect from the next line onward, but <code>@</code> is a rare example of a command that takes effect immediately. It is most commonly used in the form {{code|@echo off}} which not only switches off echoing but prevents the command line itself from being echoed.<ref>{{Cite web |title=echo |url=https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/echo |website=docs.microsoft.com |access-date=2018-09-11 |archive-date=2018-09-11 |archive-url=https://web.archive.org/web/20180911191929/https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/echo |url-status=live }}</ref><ref>{{Cite web |title=Echo - Windows CMD - SS64.com |url=https://ss64.com/nt/echo.html |website=ss64.com |access-date=2018-09-11 |archive-date=2018-09-11 |archive-url=https://web.archive.org/web/20180911191818/https://ss64.com/nt/echo.html |url-status=live }}</ref>
* In [[Windows PowerShell]], @ is used as array operator for array and hash table literals and for enclosing here-string literals.<ref>{{Cite web |title=Windows PowerShell Language Specification Version 3.0 |url=http://www.microsoft.com/en-us/download/details.aspx?id=36389 |website=Microsoft Download Center |access-date=2013-10-29 |archive-date=2022-01-26 |archive-url=https://web.archive.org/web/20220126032007/https://www.microsoft.com/en-us/download/details.aspx?id=36389 |url-status=live }}</ref>