under_scores, camelCase and PascalCase - The three naming conventions every programmer should be aware of
Tags: productivity, beginners
Published: 2019-07-10 05:31:20

The various tokens in your code (variables, classes, functions, namespaces, etc.) can be named using one of these three styles, broadly speaking:

1. Camel Case (ex: *someVar*, *someClass*, *somePackage.xyz*).
2. Pascal Case (ex: *SomeVar*, *SomeClass*, *SomePackage.xyz*).
3. Underscores (ex: *some_var*, *some_class*, *some_package.xyz*).

In camel casing, names start with a lower case but each proper word in the name is capitalized and so are acronyms. For example, commonly used tokens in many languages such as toString, checkValidity, lineHeight, timestampToLocalDateTime,  etc. are all examples of camel casing.

Pascal casing is similar to camel casing except that the first letter also starts with a capital letter (SomeClass instead of someClass).

In underscore casing, everything is in lower case (even acronyms) and the words are separated by underscores (some_class, some_func, some_var, etc). This convention is also popularly known as *snake case*.

The general idea is that you can use any convention in your project as long as you are consistent about using it everywhere. But when you code for a large project or team, you should conform to the norm of what is being used there. Hence, its helpful to be aware of the conventions typical in various programming languages.

The general practice for a C style language like Java or JS is to use camelCase for all variables and object members (properties & methods), and PascalCase for class names and constructors. Namespaces (or Packages in Java world) are usually in camelCase.

But some languages make an exception to that. C#, for example, uses PascalCase for namespaces and even public methods. Hence, the main function (or entry point) is always `static void main()` in java but `static void Main()` in C# (Note the capitalization of the word "Main").

Some languages which don't derive their syntax from C (such as Python & Ruby) use underscores for almost everything except class names. Hence, its always ` sys.base_prefix` instead of `sys.basePrefix`, `datetime` instead of `DateTime`, `str.splitlines()` instead of `str.splitLines()` in python.

In case of python's standard library, I've noticed that even the classes use underscores sometimes which is an inconsistency. For example, `datetime.datetime` is a class and so is `csv.excel_tab`. The popular frameworks and libraries though (such as django and flask) use the camel case for classes.

Similar inconsistency is in PHP. The language is evolving from underscores to camel casing in recent years but some old tokens still haunts that language. For ex, `mysqli::set_local_infile_default` vs `PDOStatement::debugDumpParams`.

So, ultimately, it comes down to your own preference when you are starting a project. But it helps to know what are the usually followed conventions in popular open source projects in the language of your preference.

**Update**

There is a fourth case too as pointed out by @ovais, namely *kebab case*. Its very much like underline casing except that the underlines are replaced with hyphens (dashes). So, `some_func` becomes `some-func` which is obviously disallowed because dash isn't used for naming tokens as its already a built-in for the minus operator in most programming languages. Where *kebab case* is used most frequently is for creating classes in your css stylesheets! Names like `main-div`, `main-navbar` and `article-footer` are commonly used by web developers while writing their HTML/CSS. This convention is basically the kebab case.

**Update**

As @patrykrudnicki says, constants are handled differently. In my experience, the full underscores (`SOME_CONST`) is a popular convention for constants in many languages including Java, PHP and Python.

**Update**

To summarize, this is the typical or generally followed convention in the most used open source programming languages:

| Token		|	python			|	Java/JS			|	PHP								|
|:----------|:------------------|:------------------|:----------------------------------|
| variable	|	under_score		|	camelCase		|	mix (moving towards camelCase)	|
| function	|	under_score()		|	camelCase()		|	mix (moving towards camelCase())	|
| constant	|	UNDER_SCORE		|	UNDER_SCORE		|	UNDER_SCORE						|
| class		|	PascalCase		|	PascalCase		|	mix (moving towards PascalCase)	|
| namespace	|	under_score		|	camelCase		|	mix (moving towards PascalCase)	|






Some helpful links:

1. <https://softwareengineering.stackexchange.com/questions/196416/whats-the-dominant-naming-convention-for-variables-in-php-camelcase-or-undersc>
2. <https://stackoverflow.com/questions/149491/pascal-casing-or-camel-casing-for-c-sharp-code>
3. <https://www.c-sharpcorner.com/forums/when-to-use-camel-case-and-pascal-case-c-sharp>
4. <https://softwareengineering.stackexchange.com/questions/53498/what-is-the-philosophy-reasoning-behind-cs-pascal-casing-method-names>