In computer programming, a naming convention is a set of rules for choosing the character sequence to be used for identifiers which denote variables, types and functions etc. in source code and documentation.
Reasons for using a naming convention (as opposed to allowing programmers to choose any character sequence) include the following:
The choice of naming conventions can be an enormously controversial issue, with partisans of each holding theirs to be the best and others to be inferior. Colloquially, this is said to be a matter of "religion".[2] Many companies have also established their own set of conventions to best meet their interests.
Contents |
Some of the potential benefits that can be obtained by adopting a naming convention include the following:
The choice of naming conventions (and the extent to which they are enforced) is often a contentious issue, with partisans holding their viewpoint to be the best and others to be inferior.
Moreover, even with known and well-defined naming conventions in place, some organizations may fail to consistently adhere to them, causing inconsistency and confusion.
These challenges may be exacerbated if the naming convention rules are internally inconsistent, arbitrary, difficult to remember, or otherwise perceived as more burdensome than beneficial.
Although largely hidden from the view of most business users, well-chosen identifiers make it significantly easier for subsequent generations of analysts and developers to understand what the system is doing and how to fix or extend the source code for new business needs.
For example, although the following:
a = b * c;
is syntactically correct, it is entirely opaque as to intent or meaning. Contrast this with:
weekly_pay = hours_worked * pay_rate;
which implies the intent and meaning of the source code, at least to those familiar with the underlying context of the application.
The exact rules of a naming convention depend on the context in which they are employed. Nevertheless, there are several common elements that influence most if not all naming conventions in common use today.
A fundamental element of all naming conventions are the rules related to identifier length (i.e., the finite number of individual characters allowed in an identifier). Some rules dictate a fixed numerical bound, while others specify less precise heuristics or guidelines.
Identifier length rules are routinely contested in practice, and subject to much debate academically.
Some considerations:
It is an open research issue whether some programmers prefer shorter identifiers because they are easier to type, or think up, than longer identifiers, or because in many situations a longer identifier simply clutters the visible code and provides no perceived additional benefit.
Brevity in programming could be in part attributed to:
Some naming conventions limit whether letters may appear in uppercase or lowercase. Other conventions do not restrict letter case, but attach a well-defined interpretation based on letter case. Some naming conventions specify whether alphabetic, numeric, or alphanumeric characters may be used, and if so, in what sequence.
A common recommendation is "Use meaningful identifiers." A single word may not be as meaningful, or specific, as multiple words. Consequently, some naming conventions specify rules for the treatment of "compound" identifiers containing more than one word.
As most programming languages do not allow whitespace in identifiers, a method of delimiting each word is needed (to make it easier for subsequent readers to interpret which characters belong to which word).
One approach is to delimit separate words with a nonalphanumeric character. The two characters commonly used for this purpose are the hyphen ('-') and the underscore ('_'), (e.g., the two-word name "two words" would be represented as "two-words" or "two_words"). The hyphen is used by nearly all programmers writing COBOL and Lisp; it is also common for selector names in Cascading Style Sheets. Most other languages (e.g., languages in the C and Pascal families) reserve the hyphen for use as the subtraction infix operator, so it is not available for use in identifiers and underscores are therefore used instead.
Another approach is to indicate word boundaries using medial capitalization (also called "CamelCase" and many other names), thus rendering "two words" as either "twoWords" or "TwoWords". This convention is commonly used in Java, C# and Visual Basic.
Some naming conventions represent rules or requirements that go beyond the requirements of a specific project or problem domain, and instead reflect a greater over-arching set of principles defined by the software architecture, underlying programming language or other kind of cross-project methodology.
Perhaps the most well-known is Hungarian notation, which encodes either the purpose ("Apps Hungarian") or the type ("Systems Hungarian") of a variable in its name.[3]
A style used for very short (8 characters and less) could be: LCCIIL01, where LC would be the application (Letters of Credit), C for COBOL, IIL for the particular process subset, and the 01 a sequence number.
This sort of convention is still in active use in mainframes dependent upon JCL and is also seen in the 8.3 (maximum 8 characters with period separator followed by 3 character file type) MS-DOS style.
One of the earliest published convention systems was IBM's "OF Language" documented in a 1980s IMS (Information Management System) manual .
It detailed the PRIME-MODIFIER-CLASS word scheme, which consisted of names like "CUST-ACT-NO" to indicate "customer account number".
PRIME words were meant to indicate major "entities" of interest to a system.
MODIFIER words were used for additional refinement, qualification and readability.
CLASS words ideally would be a very short list of data types relevant to a particular application. Common CLASS words might be: NO (number), ID (identifier), TXT (text), AMT (amount), QTY (quantity), FL (flag), CD (code), W (work) and so forth. In practice, the available CLASS words would be a list of less than two dozen terms.
CLASS words, typically positioned on the right (suffix), served much the same purpose as Hungarian notation prefixes.
The purpose of CLASS words, in addition to consistency, was to specify to the programmer the data type of a particular data field. Prior to the acceptance of BOOLEAN (two values only) fields, FL (flag) would indicate a field with only two possible values.
Adobe's Coding Conventions and Best Practices suggests naming standards for ActionScript that are mostly consistent with those of ECMAScript. The style of identifiers is similar to that of Java.
In Ada, the only recommended style of identifiers is Mixed_Case_With_Underscores.
In C and C++, keywords and standard library identifiers are mostly lowercase. In the C standard library, abbreviated names are the most common (e.g. isalnum for a function testing whether a character is alphanumeric), while the C++ standard library often uses an underscore as a word separator (e.g. out_of_range). Identifiers representing macros are, by convention, written using only upper case letters and underscores (this is related to the convention in many programming languages of using all-upper-case identifiers for constants). Names containing double underscore or beginning with an underscore and a capital letter are reserved for implementation (compiler, standard library) and should not be used (e.g. reserved__ or _Reserved).[4][5]
In Java, naming conventions for identifiers have been established and suggested by various Java communities such as Sun Microsystems,[6] Netscape,[7] AmbySoft[8] etc. A sample of naming conventions set by Sun Microsystem are listed below, where a name in "CamelCase" is one composed of a number of words joined without spaces, with each word's initial letter in capitals — for example "CamelCase".
| Identifier type | Rules for naming | Examples |
|---|---|---|
| Classes | Class names should be nouns in UpperCamelCase, with the first letter of every word capitalised. Use whole words — avoid acronyms and abbreviations (unless the abbreviation is much more widely used than the long form, such as URL or HTML). |
|
| Methods | Methods should be verbs in lowerCamelCase; that is, with the first letter lowercase and the first letters of subsequent words in uppercase. |
|
| Variables | Local variables, instance variables, and class variables are also written in lowerCamelCase. Variable names should not start with underscore (_) or dollar sign ($) characters, even though both are allowed. Certain coding conventions state that underscores should be used to prefix all instance variables, for improved reading and program understanding.
Variable names should be short yet meaningful. The choice of a variable name should be mnemonic — that is, designed to indicate to the casual observer the intent of its use. One-character variable names should be avoided except for temporary "throwaway" variables. Common names for temporary variables are i, j, k, m, and n for integers; c, d, and e for characters. |
|
| Constants | Constants should be written in uppercase characters separated by underscores. Constant names may also contain digits if appropriate, but not as the first character. |
|
Java compilers do not enforce these rules, but failing to follow them may result in confusion and erroneous code. For example, widget.expand() and Widget.expand() imply significantly different behaviours: widget.expand() implies an invocation to method expand() in an instance named widget, whereas Widget.expand() implies an invocation to static method expand() in class Widget.
One widely used Java coding style dictates that UpperCamelCase be used for classes and lowerCamelCase be used for instances and methods.[6] Recognising this usage, some IDEs, such as Eclipse, implement shortcuts based on CamelCase. For instance, in Eclipse's content assist feature, typing just the upper-case letters of a CamelCase word will suggest any matching class or method name (for example, typing "NPE" and activating content assist could suggest "NullPointerException").
Initialisms of three or more letters are CamelCase instead of upper case (e.g., "parseDbmXmlFromIPAddress" instead of "parseDBMXMLFromIPAddress"). One may also set the boundary at two or more letters (e.g., "parseDbmXmlFromIpAddress").
The built-in JavaScript libraries use the same naming conventions as Java. Classes use upper camel case (RegExp, TypeError, XMLHttpRequest, DOMObject) and methods use lower camel case (getElementById, getElementsByTagNameNS, createCDATASection). In order to be consistent most JavaScript developers follow these conventions.
Common practice in most Lisp dialects is to use dashes to separate words in identifiers, as in with-open-file and make-hash-table. Global variable names conventionally start and end with asterisks: *map-walls*.
Microsoft .NET recommends UpperCamelCase (a.k.a. "Pascal Style") for most identifiers. (lowerCamelCase is recommended for parameters and variables) and is a shared convention for the .NET languages.[9] Microsoft further recommends that no type prefix hints (also known as Hungarian notation) are used.[10] Instead of using Hungarian notation it is recommended to end the name with the base class' name; LoginButton instead of LoginBtn.[11]
Perl takes some cues from its C heritage for conventions. Locally scoped variables and subroutine names are lowercase with infix underscores. Subroutines and variables meant to be treated as private are prefixed with an underscore. Package variables are title cased. Declared constants are all caps. Package names are camel case excepting pragmata—e.g., strict and mro—which are lowercase.
Python recommends UpperCamelCase for class names, CAPITALIZED_WITH_UNDERSCORES for constants, and lowercase_separated_by_underscores for other names.[12]
Ruby recommends UpperCamelCase for class names, CAPITALIZED_WITH_UNDERSCORES for constants, and lowercase_separated_by_underscores for other names.
Visual Basic's naming conventions tend to rest on what is most human-readable, as opposed to providing information about the identifier itself.