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Leaky abstraction
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<h2 id="history">History</h2> <p>The term "leaky abstraction" was popularized in 2002 by <a href="/facts/Joel_Spolsky/VbsY6yMQ">Joel Spolsky</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> A 1992 paper by <a href="/facts/Gregor_Kiczales/68UI7JEn">Kiczales</a> describes some of the issues with imperfect abstractions and presents a potential solution to the problem by allowing for the customization of the abstraction itself.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <h2 id="effect-on-software-development">Effect on software development</h2> <p>As systems become more complex, software developers must rely upon more abstractions. Each abstraction tries to hide complexity, letting a developer write software that "handles" the many variations of modern computing. </p><p>However, this law claims that developers of <i>reliable</i> software must learn the abstraction's underlying details anyway. </p> <h2 id="examples">Examples</h2> <p>Spolsky's <a href="https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/">article</a> cites many examples of leaky abstractions that create problems for software development: </p> <ul><li>The <a href="/facts/TCP%2fIP/KNkxtSpw">TCP/IP</a> protocol stack is the combination of <a href="/facts/Transmission_Control_Protocol/WW4sPrt9">TCP</a>, which tries to provide reliable delivery of information, running on top of <a href="/facts/Internet_Protocol/Qq6VeEal">IP</a>, which provides only 'best-effort' service. When IP loses a packet, TCP has to retransmit it, which takes additional time. Thus TCP provides the abstraction of a reliable connection, but the implementation details leak through in the form of potentially variable performance (throughput and latency both suffer when data has to be retransmitted), and the connection can still break entirely.</li> <li><a href="/facts/Iterator/f0HhTBWz">Iterating</a> over a large two-dimensional <a href="/facts/Array_data_structure/BKGvF8AM">array</a> can have radically different performance if done horizontally rather than vertically, depending on the order in which elements are stored in memory. One direction may vastly increase <a href="/facts/CPU_cache/x8BYFcdv">cache misses</a> and <a href="/facts/Page_fault/0pzn9ByX">page faults</a>, both of which greatly delay access to memory.</li> <li>The <a href="/facts/SQL/UjQLJcYm">SQL</a> language abstracts away the procedural steps for querying a <a href="/facts/Database/VYcpkevb">database</a>, allowing one to merely define what one wants. But certain SQL queries are thousands of times slower than other logically equivalent queries. On an even higher level of abstraction, <a href="/facts/Object-relational_mapping/sjIPEIfq">ORM</a> systems, which isolate object-oriented code from the implementation of object persistence using a relational database, still force the programmer to think in terms of databases, tables, and native SQL queries as soon as performance of ORM-generated queries becomes a concern.</li> <li>Although network file systems like <a href="/facts/Network_File_System/jWRRALVo">NFS</a> and <a href="/facts/Server_Message_Block/pWM35pl8">SMB</a> let one treat files on remote machines as if they were local, the connection to the remote machine may slow down or break, and the file stops acting as if it were local.</li> <li>The <a href="/facts/ASP.NET/xq7KM8mN">ASP.NET</a> web forms programming platform, not to be confused with ASP.NET MVC, abstracts away the difference between compiled back-end code to handle clicking on a hyperlink (<a>) and code to handle clicking on a button. However, ASP.NET needs to hide the fact that in HTML there is no way to submit a form from a hyperlink. It does this by generating a few lines of JavaScript and attaching an <a href="/facts/DOM_events/1KoczpWr">onclick</a> handler to the hyperlink. However, if the end user has JavaScript disabled, the ASP.NET application malfunctions. Furthermore, one cannot naively think of event handlers in ASP.NET in the same way as in a desktop GUI framework such as <a href="/facts/Windows_Forms/H8VpGJxX">Windows Forms</a>; due to the asynchronous nature of the Web, processing event handlers in ASP.NET requires exchanging data with the server and reloading the form.</li></ul> <p>In 2020, <a href="/facts/Massachusetts_Institute_of_Technology/Xk49vNA8">Massachusetts Institute of Technology</a> computing science teaching staff Anish, Jose, and Jon argued that the command line interface for <a href="/facts/Git/U5Ty9QmQ">git</a> is a leaky abstraction, in which the underlying "beautiful design" of the git data model needs to be understood for effective usage of git.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Abstraction_inversion/6Mr1aHqU">Abstraction inversion</a></li> <li><a href="/facts/Dependency_inversion_principle/wkJ1aFvy">Dependency inversion principle</a></li> <li><a href="/facts/Essential_complexity/zWaekgpS">Essential complexity</a></li> <li><a href="/facts/Modular_programming/sNoqKvRD">Modular programming</a></li> <li><a href="/facts/Separation_of_concerns/Tx8jawNT">Separation of concerns</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Seibel, Peter (1 November 2006). Practical Common Lisp. Apress. p. 96. ISBN 978-1-4302-0017-8. <a href="978-1-4302-0017-8" target="_blank">978-1-4302-0017-8</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Spolsky, Joel (2002). "The Law of Leaky Abstractions". Retrieved 2010-09-22. <a href="https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/" target="_blank">https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Spolsky, Joel (2002). "The Law of Leaky Abstractions". Retrieved 2010-09-22. <a href="https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/" target="_blank">https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>arvindpdmn (2019-08-23). "Leaky Abstractions". Devopedia. Retrieved 2020-07-07. <a href="https://devopedia.org/leaky-abstractions" target="_blank">https://devopedia.org/leaky-abstractions</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Kiczales, Gregor (1992). "Towards a New Model of Abstraction in the Engineering of Software" (PDF). Archived from the original (PDF) on 2011-06-04. Retrieved 2010-02-03. <a href="https://web.archive.org/web/20110604013045/http://www2.parc.com/csl/groups/sda/publications/papers/Kiczales-IMSA92/for-web.pdf" target="_blank">https://web.archive.org/web/20110604013045/http://www2.parc.com/csl/groups/sda/publications/papers/Kiczales-IMSA92/for-web.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"Version Control (Git)". the missing semester of your cs education. Retrieved 2020-07-31. <a href="https://missing.csail.mit.edu/2020/version-control/" target="_blank">https://missing.csail.mit.edu/2020/version-control/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> </ol>