The writing formatcamel case (sometimes stylizedautologically ascamelCase orCamelCase, also known ascamel caps or more formally asmedial capitals) is the practice of writing phrases without spaces or punctuation and withcapitalized words. The format indicates the first word starting with either case, then the following words having an initial uppercase letter. Common examples includeYouTube,[1]PowerPoint,HarperCollins,FedEx,iPhone,eBay,[2] andLaGuardia.[3] Camel case is often used as anaming convention in computer programming. It is also sometimes used in online usernames such asJohnSmith, and to make multi-worddomain names more legible, for example in promotingEasyWidgetCompany.com.
The more specific termsPascal case andupper camel case refer to a joined phrase where the first letter of each word is capitalized, including the initial letter of the first word. Similarly,lower camel case (also known asdromedary case) requires an initial lowercase letter. Some people and organizations, notablyMicrosoft, use the termcamel case only for lower camel case, designating Pascal case for the upper camel case.[4] Some programming styles prefer camel case with the first letter capitalized, others not.[5][4][6] For clarity, this article leaves the definition of camel case ambiguous with respect to capitalization, and uses the more specific terms when necessary.
Camel case is distinct from several other styles:title case, which capitalizes all words but retains the spaces between them;Tall Man lettering, which uses capitals to emphasize the differences between similar-looking product names such aspredniSONE andpredniSOLONE; andsnake case, which usesunderscores interspersed with lowercase letters (sometimes with the first letter capitalized). A combination of snake and camel case (identifiersWritten_Like_This) is recommended in theAda 95 style guide.[7]
The practice has various names, including:
The earliest known occurrence of the term "InterCaps" on Usenet is in an April 1990 post to the groupalt.folklore.computers by Avi Rappoport.[22] The earliest use of the name "Camel Case" occurs in 1995, in a post by Newton Love.[23] Love has since said, "With the advent of programming languages having these sorts of constructs, the humpiness of the style made me call it HumpyCase at first, before I settled on CamelCase. I had been calling it CamelCase for years. ... The citation above was just the first time I had used the name on USENET."[24] The term "Pascal Case" was coined in design discussions for the.NET Framework, first released in 2002.[25]
The use of medial capitals as a convention in the regular spelling of everyday texts is rare, but is used in some languages as a solution to particular problems which arise when two words or segments are combined.
In Italian, pronouns can be suffixed to verbs, and because the honorific form of second-person pronouns is capitalized, this can produce a sentence likenon ho trovato il tempo di risponderLe ("I have not found time to answer you" – whereLe means "to you").
In German, many nouns denoting people lack a gender-neutral form, which is why often, especially colloquially, the male form of a noun is used generically to address everyone, regardless of their gender (this is calledgenerisches Maskulinum in German). Another, more recent approach is using the medial capital letterI, calledBinnen-I, in written text for words likeStudentInnen ("students") to indicate that bothStudenten ("male students") andStudentinnen ("female students") are referred to simultaneously. However, mid-word capitalization does not conform to theGerman orthography prescribed by theRat für deutsche Rechtschreibung (Council for German Orthography) apart from proper names likeMcDonald. In order to adhere to orthography, the introductory “students” example could be corrected usingparentheses toStudent(inn)en, which is analogous to writing "congress(wo)men" in English.[26]
InIrish, camel case is used when an inflectional prefix is attached to a proper noun, for examplei nGaillimh ("inGalway"), fromGaillimh ("Galway");an tAlbanach ("the Scottish person"), fromAlbanach ("Scottish person"); andgo hÉirinn ("to Ireland"), fromÉire ("Ireland"). In recentScottish Gaelic orthography, a hyphen has been inserted:an t-Albannach.
This convention of inflectional prefix is also used by several writtenBantu languages (e.g.isiZulu, "Zulu language") and several indigenouslanguages of Mexico (e.g.Nahuatl,Totonacan,Mixe–Zoque, and someOto-Manguean languages).
InDutch, when capitalizing the digraphij, both the letterI and the letterJ are capitalized, for example in the country nameIJsland ("Iceland").
InChinesepinyin, camel case is sometimes used for place names so that readers can more easily pick out the different parts of the name. For example, places like Beijing (北京), Qinhuangdao (秦皇岛), and Daxing'anling (大兴安岭) can be written asBeiJing,QinHuangDao, andDaXingAnLing respectively, with the number of capital letters equaling the number ofChinese characters. Writing word compounds only by the initial letter of each character is also acceptable in some cases, so Beijing can be written asBJ, Qinghuangdao asQHD, and Daxing'anling as DXAL.
In English, medial capitals are usually only found in Scottish or Irish "Mac-" or "Mc-" patronymic names, where for exampleMacDonald, McDonald, andMacdonald are common spelling variants ofMacDonald (son of Dòmhnall), and in Anglo-Norman "Fitz-" names, where for example bothFitzGerald andFitzgerald (son of Gerald) are found.
In their English style guideThe King's English, first published in 1906,H. W. andF. G. Fowler suggested that medial capitals could be used in triplecompound words wherehyphens would cause ambiguity—the examples they give areKingMark-like (as againstKing Mark-like) andAnglo-SouthAmerican (as againstAnglo-South American). However, they described the system as "too hopelessly contrary to use at present".[27]
Some French names also uses CamelCase names, such asLeBeau (surname),LaRue,DeMordaunt, and Italian namesDeRose/DeRosa.
In the scholarly transliteration of languages written in other scripts, medial capitals are used in similar situations. For example, in transliteratedHebrew,haIvri means "the Hebrew person" or "the Jew" andb'Yerushalayim means "in Jerusalem". InTibetan proper names likerLobsang, the "r" stands for a prefix glyph in the original script that functions astone marker rather than a normal letter. Another example istsIurku, a Latin transcription of theChechen term for the capping stone of the characteristicMedieval defensive towers ofChechnya andIngushetia; the letter "I" (palochka) is not actually capital, denoting aphoneme distinct from the one transcribed as "i".
Medial capitals are traditionally used in abbreviations to reflect the capitalization that the words would have when written out in full, for example in the academic titles PhD orBSc. A more recent example isNaNoWriMo, a contraction of National Novel Writing Month and the designation for both the annual event and the nonprofit organization that runs it. In German, the names of statutes are abbreviated using embedded capitals, e.g. StGB forStrafgesetzbuch (Criminal Code), PatG forPatentgesetz (Patent Act), BVerfG forBundesverfassungsgericht (Federal Constitutional Court), or the very common GmbH, forGesellschaft mit beschränkter Haftung (private limited company). In this context, there can even be three or more camel case capitals, e.g. in TzBfG forTeilzeit- und Befristungsgesetz (Act on Part-Time and Limited Term Occupations). In French, camel case acronyms such asOuLiPo (1960) were favored for a time as alternatives to initialisms.
Camel case is often used to transliterate initialisms into alphabets where two letters may be required to represent a single character of the original alphabet, e.g.,DShK fromCyrillic ДШК.
The first systematic and widespread use of medial capitals for technical purposes was the notation for chemical formulas invented by the Swedish chemistJacob Berzelius in 1813. To replace the multitude of naming and symbol conventions used by chemists until that time, he proposed to indicate each chemical element by a symbol of one or two letters, the first one being capitalized. The capitalization allowed formulas like "NaCl" to be written without spaces and still be parsed without ambiguity.[28][29]
Berzelius' system continues to be used, augmented with three-letter symbols such as "Uue" for unconfirmed or unknown elements and abbreviations for some common substituents (especially in the field of organic chemistry, for instance "Et" for "ethyl-"). This has been further extended to describe theamino acid sequences ofproteins and other similar domains.
Since the early 20th century, medial capitals have occasionally been used forcorporate names and product trademarks, such as
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In the 1970s and 1980s, medial capitals were adopted as a standard or alternativenaming convention for multi-wordidentifiers in severalprogramming languages. The precise origin of the convention in computer programming has not yet been settled. A 1954 conference proceedings[33] occasionally informally referred toIBM'sSpeedcoding system as "SpeedCo".Christopher Strachey's paper onGPM (1965),[34] shows a program that includes some medial capital identifiers, including "NextCh" and "WriteSymbol" (This was most likely the influence of theCPL language, of which Strachey was one of the designers)
Multiple-word descriptive identifiers with embedded spaces such asend of file orchar table cannot be used in most programming languages because the spaces between the words would beparsed asdelimiters betweentokens. The alternative of running the words together as inendoffile orchartable is difficult to understand and possibly misleading; for example,chartable is an English word (able to be charted), whereascharTable means a table ofchars .
Some early programming languages, notablyLisp (1958) andCOBOL (1959), addressed this problem by allowing ahyphen ("-") to be used between words of compound identifiers, as in "END-OF-FILE": Lisp because it worked well with prefix notation (a Lisp parser would not treat a hyphen in the middle of a symbol as a subtraction operator) and COBOL because its operators were individual English words. This convention remains in use in these languages, and is also common in program names entered on acommand line, as in Unix.
However, this solution was not adequate for mathematically oriented languages such asFORTRAN (1955) andALGOL (1958), which used the hyphen as an infix subtraction operator. FORTRAN ignored blanks altogether, so programmers could use embedded spaces in variable names. However, this feature was not very useful since the early versions of the language restricted identifiers to no more than six characters.
Exacerbating the problem, commonpunched card character sets of the time were uppercase only and lacked other special characters. It was only in the late 1960s that the widespread adoption of theASCII character set made both lowercase and theunderscore character_ universally available. Some languages, notablyC, promptly adopted underscores as word separators, and identifiers such asend_of_file are still prevalent in C programs and libraries (as well as in later languages influenced by C, such asPerl andPython). However, some languages and programmers chose to avoid underscores and adopted camel case instead.
Charles Simonyi, who worked atXerox PARC in the 1970s and later oversaw the creation of Microsoft's Office suite of applications, invented and taught the use ofHungarian Notation, one version of which uses the lowercase letter(s) at the start of a (capitalized) variable name to denote its type. One account[citation needed] claims that the camel case style first became popular at Xerox PARC around 1978, with theMesa programming language developed for theXerox Alto computer. This machine lacked an underscore key (whose place was taken by a left arrow "←"), and the hyphen and space characters were not permitted in identifiers, leaving camel case as the only viable scheme for readable multiword names. The PARC Mesa Language Manual (1979) included a coding standard with specific rules for upper and lower camel case that was strictly followed by the Mesa libraries and the Alto operating system.Niklaus Wirth, the inventor ofPascal, came to appreciate camel case during a sabbatical at PARC and used it inModula, his next programming language.[35]
TheSmalltalk language, which was developed originally on the Alto, also uses camel case instead of underscores. This language became quite popular in the early 1980s, and thus may also have been instrumental in spreading the style outside PARC.
Upper camel case (or "Pascal case") is used inWolfram Language in computer algebraic systemMathematica for predefined identifiers. User defined identifiers should start with a lower case letter. This avoids the conflict between predefined and user defined identifiers both today and in all future versions.
C# variable names are recommended to follow the lower camel case convention.[36]
Whatever its origins in the computing field, the convention was used in the names of computer companies and their commercial brands, since the late 1970s — a trend that continues to this day:
In the 1980s and 1990s, after the advent of the personal computer exposed hacker culture to the world, camel case then became fashionable for corporatetrade names in non-computer fields as well. Mainstream usage was well established by 1990:
During thedot-com bubble of the late 1990s, the lowercase prefixes "e" (for "electronic") and "i" (for "Internet",[37] "information", "intelligent", etc.) became quite common, giving rise to names likeApple'siMac and theeBox software platform.
In 1998, Dave Yost suggested that chemists use medial capitals to aid readability of long chemical names, e.g. write AmidoPhosphoRibosylTransferase instead ofamidophosphoribosyltransferase.[38] This usage was not widely adopted.
Camel case is sometimes used for abbreviated names of certain neighborhoods, e.g. New York City neighborhoodsSoHo (South ofHouston Street) andTriBeCa (TriangleBelowCanal Street) and San Francisco'sSoMa (South ofMarket). Such usages erode quickly, so the neighborhoods are now typically rendered asSoho,Tribeca, andSoma.
Internal capitalization has also been used for other technical codes likeHeLa (1983).
The use of medial caps for compound identifiers is recommended by thecoding style guidelines of many organizations or software projects. For some languages (such asMesa,Pascal,Modula,Java andMicrosoft's.NET) this practice is recommended by the language developers or by authoritative manuals and has therefore become part of the language's "culture".
Style guidelines often distinguish between upper and lower camel case, typically specifying which variety should be used for specific kinds of entities:variables,record fields,methods,procedures,functions,subroutines,types, etc. These rules are sometimes supported bystatic analysis tools that checksource code for adherence.
The originalHungarian notation for programming, for example, specifies that a lowercase abbreviation for the "usage type" (not data type) should prefix all variable names, with the remainder of the name in upper camel case; as such it is a form of lower camel case.
Programming identifiers often need to containacronyms and initialisms that are already in uppercase, such as "old HTML file". By analogy with the title case rules, the natural camel case rendering would have the abbreviation all in uppercase, namely "oldHTMLFile". However, this approach is problematic when two acronyms occur together (e.g., "parse DBM XML" would become "parseDBMXML") or when the standard mandates lower camel case but the name begins with an abbreviation (e.g. "SQL server" would become "sQLServer"). For this reason, some programmers prefer to treat abbreviations as if they were words and write "oldHtmlFile", "parseDbmXml" or "sqlServer".[39] However, this can make it harder to recognize that a given word is intended as an acronym.[40]
Difficulties arise when identifiers have different meaning depending only on the case, as can occur with mathematical functions or trademarks. In this situation changing the case of an identifier might not be an option and an alternative name need be chosen.
Camel case is used in somewiki markup languages for terms that should be automatically linked to otherwiki pages. This convention was originally used inWard Cunningham's originalwiki software,WikiWikiWeb,[41] and can be activated in most other wikis. Some wiki engines such asTiddlyWiki,Trac andPmWiki make use of it in the default settings, but usually also provide a configuration mechanism orplugin to disable it. Wikipedia formerly used camel case linking as well, but switched to explicit link markup usingsquare brackets[42] and many other wiki sites have done the same.MediaWiki, for example,does not support camel case for linking. Some wikis that do not use camel case linking may still use the camel case as a naming convention, such asAboutUs.
TheNIEM registry requires thatXML data elements use upper camel case and XML attributes use lower camel case.
Most popularcommand-line interfaces andscripting languages cannot easily handle file names that contain embedded spaces (usually requiring the name to be put in quotes). Therefore, users of those systems often resort to camel case (or underscores, hyphens and other "safe" characters) for compound file names likeMyJobResume.pdf.
Microblogging andsocial networking services that limit the number of characters in a message are potential outlets for medial capitals. Using camel case between words reduces the number of spaces, and thus the number of characters, in a given message, allowing more content to fit into the limited space.Hashtags, especially long ones, often use camel case to maintain readability (e.g. #CollegeStudentProblems is easier to read than #collegestudentproblems);[43] this practice improvesaccessibility asscreen readers recognize CamelCase in parsing composite hashtags.[44]
In website URLs, spaces arepercent-encoded as "%20", making the address longer and lesshuman readable. By omitting spaces, camel case does not have this problem.
Camel case has been criticized as negatively impacting readability due to the removal of spaces and uppercasing of every word.[45]
A 2009 study of 135 subjects comparingsnake case (underscored identifiers) to camel case found that camel case identifiers were recognized with higher accuracy among all subjects. Subjects recognized snake case identifiers more quickly than camel case identifiers. Training in camel case sped up camel case recognition and slowed snake case recognition, although this effect involved coefficients with highp-values. The study also conducted a subjective survey and found that non-programmers either preferred underscores or had no preference, and 38% of programmers trained in camel case stated a preference for underscores. However, these preferences had no statistical correlation to accuracy or speed when controlling for other variables.[46]
A 2010 follow-up study used a similar study design with 15 subjects consisting of expert programmers trained primarily in snake case. It used a static rather than animated stimulus and found perfect accuracy in both styles except for one incorrect camel case response. Subjects recognized identifiers in snake case more quickly than camel case. The study used eye-tracking equipment and found that the difference in speed for its subjects was primarily due to the fact that average duration offixations for camel-case was significantly higher than that of snake case for 3-part identifiers. The survey recorded a mixture of preferred identifier styles but again there was no correlation of preferred style to accuracy or speed.[47]
{{cite book}}:ISBN / Date incompatibility (help)In terms of camel-cased identifiers, this has a greater impact on identifiers that include short words and especially acronyms. For example, consider the acronym ID found in the identifier kIOuterIIDPath. Because of the run of uppercase letters, the task of reading kIOuterIIDPath, in particular the identification of the word ID, is more difficult.
The experiment builds on past work of others who study how readers of natural language perform such tasks. Results indicate that camel casing leads to higher accuracy among all subjects regardless of training, and those trained in camel casing are able to recognize identifiers in the camel case style faster than identifiers in the underscore style.
An empirical study to determine if identifier-naming conventions (i.e., camelCase and under_score) affect code comprehension is presented. An eye tracker is used to capture quantitative data from human subjects during an experiment. The intent of this study is to replicate a previous study published at ICPC 2009 (Binkley et al.) that used a timed response test method to acquire data. The use of eye-tracking equipment gives additional insight and overcomes some limitations of traditional data gathering techniques. Similarities and differences between the two studies are discussed. One main difference is that subjects were trained mainly in the underscore style and were all programmers. While results indicate no difference in accuracy between the two styles, subjects recognize identifiers in the underscore style more quickly.
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