Constants

How to create constants? (kinda)#

FRUIT = "orange"
  • Anything that starts with uppercase is a constant in Ruby.
  • They are constants because the first letter is uppercase.
Array
String
Hash
  • A constant doesn’t require any special symbol or syntax to declare. You just need to make the first letter an uppercase letter.
  • These are all valid constants:
ABC = 1
Goo = 2
Foo = 3

Constants can change 🤷#

  • Constants are mutable in ruby.
  • Constants can changes 🤷... but you will get an warning:
[1] pry(main)> COUNT = 2
=> 2
[2] pry(main)> COUNT = 3
(pry):2: warning: already initialized constant COUNT
(pry):1: warning: previous definition of COUNT was here
=> 3
[3] pry(main)> COUNT
=> 3
[4] pry(main)>
  • There is no way to prevent a constants from changing 😱
  • Because variables in Ruby are not containers, they are simply pointers to objects. Or labels, if you prefer.

Can't defined constants inside a method:#

[4] pry(main)> def my_method
[4] pry(main)* COUNT = 2
[4] pry(main)* end
(eval):3: dynamic constant assignment
COUNT = 2
^~~~~
[4] pry(main)> my_method
NameError: undefined local variable or method `my_method' for main:Object
Did you mean? method
from (pry):4:in `__pry__'

Class assigned to a constant#

  • When you define a class, what you’re really doing is creating a Class object, which is assigned to a constant.
  • The constant becomes the class name.
  • No real constants in Ruby. 🤦
Edit this page