Ruby: Sigils (Function and Variable Name Conventions)

By Xah Lee. Date: 2022-12-27.

Sigils are characters added in front or after a function/variable name that indicates the purpose of the function or variable.

In ruby, these sigils are not enforced by Ruby compiler.

Function Naming Conventions

Function Naming
Name	Explanation
`…?`	the function returns true or false. (the function is a predicate.)
`…!`	the function modifies the variable argument.

# function ending in ? but ruby does not enforce it to return boolean
def f?(x) x+1 end

p f?(4) == 5

Variable Naming
Name prefix	Explanation
`a…z`	lower case = local variable. [see Ruby: Variable]
`A…Z`	upper case = Constant
`_`	a dummy variable that is not used but required by syntax, such as loop thru index and value of a array.
`$`	global variable [see Ruby: List of Predefined Global Variables]
`@`	instance variable (of a class in OOP)
`@@`	class variable (of a class in OOP)

# sigils are not strictly enforced

@x = 0
_ = 0
_x = 0
d = 0
B = 1
B = 0 # gives a warning

p((@x + _ + _x  + d + B == 0) == true)