变量命名三种方式 CamelCase, snake_case, spinal-case（English version）

When it comes to naming resources in a program, there are 3 main types of case conventions: CamelCase, snake_case, and spinal-case. They are just a way of naming the resources to resemble natural language, while avoiding spaces, apostrophes and other exotic characters. This habit is universal in programming languages where only a finite set of characters is authorized for names.

CamelCase has been popularized by the Java language. It intends to emphasize the beginning of each word by making the first letter uppercase. E.g. CamelCase, CurrentUser, AddAttributeToGroup, etc. Aside from debates about its readability, its main drawback is to be ineffective in contexts which are not case sensitive.
Two variants coexist:
lowerCamelCase: where lowercase is used for the first letter.
UpperCamelCase: where the first letter is capital.

snake_case has been widely used for years by C programmers, and more recently in Ruby. Words are separated by underscores “_”, thus letting a compiler or an interpreter understand it as a single symbol, but also allowing readers to separate words fluently. However, its popularity has decreased due to a lot of abuses in C programs with over-extended or too short names. Unlike camel case, there are very few contexts where snake case is not usable. Examples: snake_case, current_user, add_attribute_to_group, etc.

spinal-case is a variant of snake case which uses hyphens “-” to separate words. The pros and cons are quite similar to those of snake case, with the exception that some languages do not allow hyphens in symbol names (for variable, class, or function naming). You may find it referred to as lisp-case because it is the usual way to name variables and functions in lisp dialects. It is also the traditional way of naming folders and files in UNIX and Linux systems. Examples: spinal-case, current-user, add-attribute-to-group, etc.

These 3 cases have their variants, based on criteria such as first letter case, behavior with accents or other special characters. Using English is recommended, to avoid special characters.