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| developer =
| typing = [[Static typing|static]], [[Strong and weak typing|strong]], [[Type safety|safe]], [[Nominal type system|nominal]]
| implementations = AdaCore [[GNAT]],<ref>{{Cite web|url=https://www.adacore.com/download|title=Commercial software solutions for Ada, C and C++|website=AdaCore|
| dialects = [[SPARK (programming language)|SPARK]], [[Ravenscar profile]]
| influenced = [[C++]], [[Chapel (programming language)|Chapel]],<ref>{{cite web|title=Chapel spec (Acknowledgements)|url=http://chapel.cray.com/spec/spec-0.98.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://chapel.cray.com/spec/spec-0.98.pdf |archive-date=2022-10-09 |url-status=live|date=2015-10-01|access-date=2016-01-14|publisher=Cray Inc}}</ref> [[Drago (programming language)|Drago]],<ref>{{cite web|url=http://www.iuma.ulpgc.es/users/gsd/Drago/|title=Drago|access-date=2018-08-06|archive-date=2020-09-14|archive-url=https://web.archive.org/web/20200914212150/http://www.iuma.ulpgc.es/users/gsd/Drago/
| license =
| released = {{Start date and age|1980|02}}
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'''Ada''' is a [[structured programming|structured]], [[statically typed]], [[Imperative programming|imperative]], and [[Object-oriented programming|object-oriented]] [[high-level programming language]], inspired by [[Pascal (programming language)|Pascal]] and other languages. It has built-in language support for ''[[design by contract]]'' (DbC), extremely [[Strong and weak typing|strong typing]], explicit concurrency, tasks, synchronous [[message passing]], protected [[Object (computer science)|objects]], and [[nondeterministic programming|non-determinism]]. Ada improves code safety and maintainability by using the [[compiler]] to find errors in favor of [[Runtime (program lifecycle phase)|runtime]] errors. Ada is an [[International standard|international]] [[technical standard]], jointly defined by the [[International Organization for Standardization]] (ISO), and the [[International Electrotechnical Commission]] (IEC). {{As of|May 2023}}, the standard, ISO/IEC 8652:2023, is called Ada 2022 informally.<ref name="ada-letters-june2023">{{cite journal |last1=Pinho |first1=Luis Miguel |title=From the Editor's Desk |journal=Ada Letters |volume=XLIII |number=1 |publisher=Association for Computing Machinery |date=June 2023 |page=3 |doi=10.1145/3631483 |doi-broken-date=1 November 2024 |url=https://dl.acm.org/action/showFmPdf?doi=10.1145%2F3631483}}</ref>
Ada was originally designed by a team led by French [[computer scientist]] [[Jean Ichbiah]] of [[Groupe Bull|Honeywell]] under contract to the [[United States Department of Defense]] (DoD) from 1977 to 1983 to supersede over 450 programming languages then used by the DoD.<ref>{{cite web|title=The Ada Programming Language|url=http://groups.engin.umd.umich.edu/CIS/course.des/cis400/ada/ada.html|website=University of Mich|access-date=27 May 2016
== Features ==
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Ada is designed for developing very large software systems. Ada packages can be compiled separately. Ada package specifications (the package interface) can also be compiled separately without the implementation to check for consistency. This makes it possible to detect problems early during the design phase, before implementation starts.
A large number of [[Compile time|compile-time]] checks are supported to help avoid bugs that would not be detectable until run-time in some other languages or would require explicit checks to be added to the source code. For example, the syntax requires explicitly named closing of blocks to prevent errors due to mismatched end tokens. The adherence to strong typing allows detecting many common software errors (wrong parameters, range violations, invalid references, mismatched types, etc.) either during compile-time, or otherwise during run-time. As concurrency is part of the language specification, the [[compiler]] can in some cases detect potential [[Deadlock (computer science)|deadlocks.]]<ref>{{cite
Ada also supports [[Runtime system|run-time]] checks to protect against access to unallocated memory, [[buffer overflow]] errors, range violations, [[off-by-one error]]s, array access errors, and other detectable bugs. These checks can be disabled in the interest of runtime efficiency, but can often be compiled efficiently. It also includes facilities to help [[software verification|program verification]]. For these reasons, Ada is sometimes used in critical systems, where any [[anomaly in software|anomaly]] might lead to very serious consequences, e.g., accidental death, injury or severe financial loss. Examples of systems where Ada is used include [[avionics]], [[air traffic control]], [[Rail transport|railways]], banking, military and [[space technology]].<ref>{{cite web|title=Ada helps churn out less-buggy code|url=http://gcn.com/Articles/1999/06/30/Ada-helps-churn-out-lessbuggy-code.aspx|publisher=Government Computer News|access-date=2010-09-14|last1=Taft|first1=S. Tucker|last2=Olsen|first2=Florence|pages=2–3|date=1999-06-30|archive-date=2015-08-31|archive-url=https://web.archive.org/web/20150831211902/http://gcn.com/Articles/1999/06/30/Ada-helps-churn-out-lessbuggy-code.aspx
{{anchor|Access type}}Ada's dynamic [[memory management]] is high-level and type-safe. Ada has no generic or untyped [[Pointer (computer programming)|pointers]]; nor does it implicitly declare any pointer type. Instead, all dynamic memory allocation and deallocation must occur via explicitly declared ''access types''. Each access type has an associated ''storage pool'' that handles the low-level details of memory management; the programmer can either use the default storage pool or define new ones (this is particularly relevant for [[Non-Uniform Memory Access]]). It is even possible to declare several different access types that all designate the same type but use different storage pools. Also, the language provides for ''accessibility checks'', both at compile time and at run time, that ensures that an ''access value'' cannot outlive the type of the object it points to.<ref>[https://youtube.com/watch?v=RyY01fRyGhM&t=419 no safe dynamic memory management in ADA], in: Writing Linux Kernel Modules in Safe Rust – Geoffrey Thomas & Alex Gaynor, The Linux Foundation, 2019-10-02</ref>
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== History ==
In the 1970s the [[United States Department of Defense|US Department of Defense]] (DoD) became concerned by the number of different programming languages being used for its embedded computer system projects, many of which were obsolete or hardware-dependent, and none of which supported safe modular programming. In 1975, a [[working group]], the [[High Order Language Working Group]] (HOLWG), was formed with the intent to reduce this number by finding or creating a programming language generally suitable for the department's and the [[Ministry of Defence (United Kingdom)|UK Ministry of Defence]]'s requirements. After many iterations beginning with an original [[Straw man proposal|straw-man proposal]]<ref>{{Cite web|url=http://iment.com/maida/computer/requirements/strawman.htm|title=DoD – Strawman Requirements – April 1975|website=iment.com|
HOLWG crafted the '''<span class="anchor" id="Steelman language requirements">Steelman language requirements</span>''' , a series of documents stating the requirements they felt a programming language should satisfy. Many existing languages were formally reviewed, but the team concluded in 1977 that no existing language met the specifications. The requirements were created by the [[United States Department of Defense]] in ''The Department of Defense Common High Order Language program'' in 1978. The predecessors of this document were called, in order, "Strawman", "Woodenman", "Tinman" and "Ironman".<ref>Department of Defense (June 1978), [https://web.archive.org/web/20200914235620/https://dwheeler.com/steelman/steelman.htm Requirements for High Order Computer Programming Languages: "Steelman"]</ref> The requirements focused on the needs of [[embedded systems|embedded]] computer applications, and emphasised reliability, maintainability, and efficiency. Notably, they included [[exception handling]] facilities, [[run-time checking]], and [[parallel computing]].
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Ada attracted much attention from the programming community as a whole during its early days. Its backers and others predicted that it might become a dominant language for general purpose programming and not only defense-related work.<ref name="sward" /> Ichbiah publicly stated that within ten years, only two programming languages would remain: Ada and [[Lisp (programming language)|Lisp]].<ref name="SIGAda-Rosen">{{cite journal |last=Rosen |first=J-P. |title=The Ada Paradox(es) |journal=Ada Letters |publisher=ACM SIGAda |volume=24 |issue=2 |date=August 2009 |pages=28–35|doi=10.1145/1620593.1620597 |s2cid=608405}}</ref> Early Ada compilers struggled to implement the large, complex language, and both compile-time and run-time performance tended to be slow and tools primitive.<ref name="sward" /> Compiler vendors expended most of their efforts in passing the massive, language-conformance-testing, government-required [[Ada Compiler Validation Capability]] (ACVC) validation suite that was required in another novel feature of the Ada language effort.<ref name="SIGAda-Rosen" />
The first validated Ada implementation was the NYU Ada/Ed translator,<ref>{{cite web |url=http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA136759 |title=Ada Compiler Validation Summary Report: NYU Ada/ED, Version 19.7 V-001 |author=SofTech Inc. |place=Waltham, MA |date=1983-04-11 |access-date=2010-12-16 |archive-url=https://web.archive.org/web/20120312080046/http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA136759 |archive-date=2012-03-12
In 1991, the US Department of Defense began to require the use of Ada (the ''Ada mandate'') for all software,<ref>{{cite web|url=http://archive.adaic.com/pol-hist/policy/mandate.txt |title=The Congressional Ada Mandate |author=Ada Information Clearinghouse |date=1994 |access-date=2015-06-07
By the late 1980s and early 1990s, Ada compilers had improved in performance, but there were still barriers to fully exploiting Ada's abilities, including a tasking model that was different from what most real-time programmers were used to.<ref name="SIGAda-Rosen" />
Because of Ada's [[Safety-critical system|safety-critical]] support features, it is now used not only for military applications, but also in commercial projects where a software bug can have severe consequences, e.g., [[avionics]] and [[air traffic control]], commercial rockets such as the [[Ariane (rocket family)|Ariane 4 and 5]], [[satellite]]s and other space systems, railway transport and banking.<ref name="Ada_usage" />
For example, the [[Primary Flight Control System]], the [[Aircraft flight control systems|fly-by-wire]] system software in the [[Boeing 777]], was written in Ada, as were the fly-by-wire systems for the aerodynamically unstable [[Eurofighter Typhoon]],<ref>{{cite web |date=16 June 1999 |title=Agile thinking |url=https://www.flightglobal.com/agile-thinking/26933.article |url-status=live |archive-url=https://web.archive.org/web/20210415054346/https://www.flightglobal.com/agile-thinking/26933.article |archive-date=15 April 2021 |access-date=13 Feb 2024 |website=FlightGlobal}}</ref> [[Saab JAS 39 Gripen|Saab Gripen]],<ref>{{Cite web |last=Frisberg |first=Bo |title=Usage of Ada in the Gripen Flight Control System |url=https://www.sigada.org/conf/sa98/papers/frisberg.pdf |url-status=live |archive-url=https://web.archive.org/web/20240115002036/https://www.sigada.org/conf/sa98/papers/frisberg.pdf |archive-date=15 Jan 2024 |access-date=13 Feb 2024 |website=The Special Interest Group on Ada}}</ref> [[Lockheed Martin F-22 Raptor]] and the DFCS replacement flight control system for the [[Grumman F-14 Tomcat]]. The Canadian Automated Air Traffic System was written in 1 million lines of Ada ([[Source lines of code|SLOC]] count). It featured advanced [[distributed processing]], a distributed Ada database, and object-oriented design. Ada is also used in other air traffic systems, e.g., the UK's next-generation Interim Future Area Control Tools Support ({{proper name|iFACTS}}) air traffic control system is designed and implemented using [[SPARK (programming language)|SPARK]] Ada.<ref>{{cite web|last=AdaCore|title=GNAT Pro Chosen for UK's Next Generation ATC System|url=http://www.adacore.com/2007/06/19/adacore-gnat-pro-chosen-for-uk-next-generation/|access-date=2011-03-01|archive-url=https://web.archive.org/web/20101224163518/http://www.adacore.com/2007/06/19/adacore-gnat-pro-chosen-for-uk-next-generation/|archive-date=2010-12-24
It is also used in the [[France|French]] [[Transmission Voie-Machine|TVM]] in-[[cab signalling]] system on the [[TGV]] high-speed rail system, and the metro suburban trains in Paris, London, Hong Kong and New York City.<ref name="Ada_usage" /><ref>{{cite web|last=AdaCore|title=Look Who's Using Ada|url=http://www.adacore.com/home/ada_answers/lookwho/|access-date=2011-03-01|archive-url=https://web.archive.org/web/20101224102110/http://www.adacore.com/home/ada_answers/lookwho|archive-date=2010-12-24
The Ada 95 revision of the language went beyond the Steelman requirements, targeting general-purpose systems in addition to embedded ones, and adding features supporting [[object-oriented programming]].<ref>David A. Wheeler (1997), [https://web.archive.org/web/20200914235617/https://dwheeler.com/steelman/steeltab.htm "Ada, C, C++, and Java vs. The Steelman"]. Originally published in ''Ada Letters'' July/August 1997</ref>
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</syntaxhighlight>
Types can have modifiers such as ''limited, abstract, private'' etc. Private types do not show their inner structure; objects of limited types cannot be copied.<ref>{{cite web |title=Ada Syntax Card |url=http://www.digilife.be/quickreferences/QRC/Ada%20Syntax%20Card.pdf |access-date=28 February 2011
=== Control structures ===
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=== Pragmas ===
A pragma is a [[compiler directive]] that conveys information to the compiler to allow specific manipulating of compiled output.<ref>{{cite web |url=http://archive.adaic.com/standards/83lrm/html/lrm-02-08.html#2.8 |title=Ada 83 LRM, Sec 2.8: Pragmas |publisher=Archive.adaic.com |access-date=2014-01-27}}</ref> Certain pragmas are built into the language,<ref>{{cite web |url=http://archive.adaic.com/standards/83lrm/html/lrm-B.html |title=Ada 83 LRM, Appendix/Annex B: Predefined Language Pragmas |publisher=Archive.adaic.com |access-date=2014-01-27
Examples of common usage of compiler pragmas would be to disable certain features, such as run-time type checking or array subscript boundary checking, or to instruct the compiler to insert object code instead of a function call (as C/C++ does with [[inline function]]s).
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=== Rationale ===
These documents have been published in various forms, including print.
* {{citation |url=http://archive.adaic.com/standards/83rat/html/Welcome.html |last1=Ichbiah |first1=Jean D. |author-link=Jean Ichbiah |last2=Barnes |first2=John G. P. |last3=Firth |first3=Robert J. |last4=Woodger |first4=Mike |title=Rationale for the Design of the Ada Programming Language |year=1986
* {{citation |url=http://www.adaic.org/resources/add_content/standards/95rat/rat95html/rat95-contents.html |last=Barnes |first=John G. P. |title=Ada 95 rationale: the language: the standard libraries |year=1995}}
* {{citation |url=http://www.adaic.org/standards/05rat/html/Rat-TTL.html |first=John |last=Barnes |title=Rationale for Ada 2005 |orig-
=== Books ===
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