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A leaky abstraction in software development refers to a design flaw where an abstraction, intended to simplify and hide the underlying complexity of a system, fails to completely do so. This results in some of the implementation details becoming exposed or 'leaking' through the abstraction, forcing users to have knowledge of these underlying complexities to effectively use or troubleshoot the system.^[1]

The concept was popularized by Joel Spolsky, who coined the term Law of Leaky Abstractions which states:^[2]

All non-trivial abstractions, to some degree, are leaky.

This means that even well-designed abstractions may not fully conceal their inner workings, and as computer systems grow more complex, the likelihood of such leaks increases. These leaks can lead to performance issues, unexpected behavior, and increased cognitive load on software developers, who are forced to understand both the abstraction and the underlying details it was meant to hide. This highlights a cause of software defects: the reliance of the software developer on an abstraction's infallibility. Despite their imperfections, abstractions are crucial in software development for managing complexity, even though they are not always flawless.

History

The term "leaky abstraction" was popularized in 2002 by Joel Spolsky.^[2]^[3] A 1992 paper by Kiczales 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.^[4]

Effect on software development

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.

However, this law claims that developers of reliable software must learn the abstraction's underlying details anyway.

Examples

Spolsky's article cites many examples of leaky abstractions that create problems for software development:

The TCP/IP protocol stack is the combination of TCP, which tries to provide reliable delivery of information, running on top of IP, 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.
Iterating over a large two-dimensional array 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 cache misses and page faults, both of which greatly delay access to memory.
The SQL language abstracts away the procedural steps for querying a database, 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, ORM 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.
Although network file systems like NFS and SMB 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.
The ASP.NET 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 onclick 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 Windows Forms; due to the asynchronous nature of the Web, processing event handlers in ASP.NET requires exchanging data with the server and reloading the form.

In 2020, Massachusetts Institute of Technology computing science teaching staff Anish, Jose, and Jon argued that the command line interface for git is a leaky abstraction, in which the underlying "beautiful design" of the git data model needs to be understood for effective usage of git.^[5]

References

^ Seibel, Peter (1 November 2006). Practical Common Lisp. Apress. p. 96. ISBN 978-1-4302-0017-8.
^ ^a ^b Spolsky, Joel (2002). "The Law of Leaky Abstractions". Retrieved 2010-09-22.
^ arvindpdmn (2019-08-23). "Leaky Abstractions". Devopedia. Retrieved 2020-07-07.
^ 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.
^ "Version Control (Git)". the missing semester of your cs education. Retrieved 2020-07-31.

[1] Seibel, Peter (1 November 2006). Practical Common Lisp. Apress. p. 96. ISBN 978-1-4302-0017-8.

[joel-2] Spolsky, Joel (2002). "The Law of Leaky Abstractions". Retrieved 2010-09-22.

[3] rvindpdmn (2019-08-23). "Leaky Abstractions". Devopedia. Retrieved 2020-07-07.

[4] 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.

[5] "Version Control (Git)". the missing semester of your cs education. Retrieved 2020-07-31.

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+{{Short description|Faulty software abstraction}}
 {{Refimprove|date=March 2011}}
-In [[software development]], a '''leaky abstraction''' is an [[Abstraction (computer science)|abstraction]] that requires knowledge of an underlying complexity to be able to effectively be used. This is an issue, as the whole point of an abstraction is to be able to abstract away these details from the user. An exaggerated example would be having to know the type of thermal paste that was used when soldering on your the processor inside of your computer to be able to interface (or use) with that computer.
+A '''leaky abstraction''' in [[software development]] refers to a design flaw where an [[Abstraction (computer science)|abstraction]], intended to simplify and hide the underlying complexity of a system, fails to completely do so. This results in some of the implementation details becoming exposed or 'leaking' through the abstraction, forcing users to have knowledge of these underlying complexities to effectively use or troubleshoot the system.<ref>{{cite book|author=Seibel, Peter |title=Practical Common Lisp|url=https://books.google.com/books?id=dVJvr8PtCMUC&pg=PA96|date=1 November 2006|publisher=Apress|isbn=978-1-4302-0017-8|page=96}}</ref>
-==History==
-The term "leaky abstraction" was popularized in 2002 by [[Joel Spolsky]].<ref>{{cite web|last=Spolsky|first=Joel|url=http://www.joelonsoftware.com/articles/LeakyAbstractions.html|year=2002|accessdate=2010-09-22|title=The Law of Leaky Abstractions}} - a blog post by Spolsky that asserts that all non-trivial abstractions are 'leaky' and therefore problematic.</ref> An earlier paper by [[Gregor Kiczales|Kiczales]] 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.<ref>{{cite web|last=Kiczales |first= Gregor |url=http://www2.parc.com/csl/groups/sda/publications/papers/Kiczales-IMSA92/for-web.pdf|year=1992|accessdate=2010-02-03| title=Towards a New Model of Abstraction in the Engineering of Software}} - a paper by Gregor Kiczales that describes the problem of imperfect abstractions and suggests a programming model for coping with them.</ref>
-==The Law of Leaky Abstractions==
+The concept was popularized by [[Joel Spolsky]], who coined the term '''Law of Leaky Abstractions''' which states:<ref name="joel" />
-As coined by Spolsky, the '''Law of Leaky Abstractions''' states:
-{{Cquote|All non-trivial abstractions, to some degree, are leaky.}}
+{{Cquote|All non-trivial abstractions, to some degree, are leaky.
+}}
+This means that even well-designed abstractions may not fully conceal their inner workings, and as computer systems grow more complex, the likelihood of such leaks increases. These leaks can lead to performance issues, unexpected behavior, and increased cognitive load on [[software developers]], who are forced to understand both the abstraction and the underlying details it was meant to hide. This highlights a cause of software defects: the reliance of the software developer on an abstraction's infallibility. Despite their imperfections, abstractions are crucial in software development for managing complexity, even though they are not always flawless.
-This statement highlights a particularly problematic cause of software defects: the reliance of the software developer on an abstraction's infallibility.
+==History==
-Spolsky's article gives examples of an abstraction that works most of the time, but where a detail of the underlying complexity cannot be ignored, thus leaking complexity out of the abstraction back into the software that uses the abstraction.
+The term "leaky abstraction" was popularized in 2002 by [[Joel Spolsky]].<ref name="joel">{{cite web|last=Spolsky|first=Joel|url=https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/|year=2002|accessdate=2010-09-22|title=The Law of Leaky Abstractions}}</ref><ref>{{Cite web|last=arvindpdmn|date=2019-08-23|title=Leaky Abstractions|url=https://devopedia.org/leaky-abstractions|access-date=2020-07-07|website=Devopedia|language=en-gb}}</ref> A 1992 paper by [[Gregor Kiczales|Kiczales]] 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.<ref>{{cite web|last=Kiczales|first=Gregor|url=http://www2.parc.com/csl/groups/sda/publications/papers/Kiczales-IMSA92/for-web.pdf|year=1992|accessdate=2010-02-03|title=Towards a New Model of Abstraction in the Engineering of Software|archive-url=https://web.archive.org/web/20110604013045/http://www2.parc.com/csl/groups/sda/publications/papers/Kiczales-IMSA92/for-web.pdf|archive-date=2011-06-04|url-status=dead}}</ref>
 ==Effect on software development==
-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.
+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.
 However, this law claims that developers of ''reliable'' software must learn the abstraction's underlying details anyway.
 ==Examples==
-Spolsky's article cites many examples of leaky abstractions that create problems for software development:
+Spolsky's [https://www.joelonsoftware.com/2002/11/11/the-law-of-leaky-abstractions/ article] cites many examples of leaky abstractions that create problems for software development:
-*The [[TCP/IP]] protocol stack is the combination of [[Transmission Control Protocol|TCP]], which tries to provide reliable delivery of information, running on top of [[Internet Protocol|IP]], 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).
+* The [[TCP/IP]] protocol stack is the combination of [[Transmission Control Protocol|TCP]], which tries to provide reliable delivery of information, running on top of [[Internet Protocol|IP]], 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.
-*[[Iterator|Iterating]] over a large two-dimensional [[Array data structure|array]] 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 [[CPU cache#Cache_miss|cache misses]] and [[page fault]]s, both of which greatly delay access to memory.
+* [[Iterator|Iterating]] over a large two-dimensional [[Array data structure|array]] 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 [[CPU cache#Cache_miss|cache misses]] and [[page fault]]s, both of which greatly delay access to memory.
-*The [[SQL]] language abstracts away the procedural steps for querying a [[database]], allowing one to merely define what one wants. But certain SQL queries are thousands of times slower than other logically equivalent queries.{{citation needed|date=May 2018}} On an even higher level of abstraction, [[Object-relational mapping|ORM]] 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.
+* The [[SQL]] language abstracts away the procedural steps for querying a [[database]], 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, [[Object-relational mapping|ORM]] 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.
-*Although network file systems like [[Network File System|NFS]] and [[Server Message Block|SMB]] 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.
+* Although network file systems like [[Network File System|NFS]] and [[Server Message Block|SMB]] 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.
-*The [[ASP.NET]] web forms programming platform, not to be confused with ASP.NET MVC, abstracts away the difference between HTML 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 [[DOM_events#Common.2FW3C_events|onclick]] 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 [[Windows Forms]]; due to the asynchronous nature of the Web, processing event handlers in ASP.NET requires exchanging data with the server and reloading the form.
+* The [[ASP.NET]] 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 (<code><a></code>) 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 [[DOM_events#Common.2FW3C_events|onclick]] 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 [[Windows Forms]]; due to the asynchronous nature of the Web, processing event handlers in ASP.NET requires exchanging data with the server and reloading the form.
+<!-- For this entire section, the citation is Spolsky's article. Recall the header is "Spolsky's article cites many examples of leaky abstractions that create problems for software development:". No need to add a cite needed template. If it isn't in his article it should be removed! -->
+In 2020, [[Massachusetts Institute of Technology]] computing science teaching staff Anish, Jose, and Jon argued that the command line interface for [[git]] is a leaky abstraction, in which the underlying "beautiful design" of the git data model needs to be understood for effective usage of git.<ref>{{Cite web|title=Version Control (Git)|url=https://missing.csail.mit.edu/2020/version-control/|access-date=2020-07-31|website=the missing semester of your cs education|language=en}}</ref>
-== See also ==
+==See also==
-*[[Abstraction inversion]]
+* [[Abstraction inversion]]
-*[[Dependency inversion principle]]
+* [[Dependency inversion principle]]
-*[[Essential complexity]]
+* [[Essential complexity]]
-*[[Modular programming]]
+* [[Modular programming]]
-*[[Separation of concerns]]
+* [[Separation of concerns]]
-== References ==
+==References==
+{{Reflist}}
-<references/>
 {{DEFAULTSORT:Leaky Abstraction}}