Illustrated Ruby: Constants

Constants in Ruby are surprising when compared to other languages. Let’s walk through a few examples to clear it up.
Here we define a constant. The name must start with a capital.	`LIST = [1, 2] p LIST`
As with variables, constants are references so their value can be mutated.	`LIST << 3 p LIST`
To protect from mutation, we can freeze the value. Attempting to mutate the value would then raise `FrozenError`.	`LIST.freeze`
Constants can be reassigned, although this emits a runtime warning. Freezing, being a property of the referenced value, does not protect from reassignment.	`LIST = [4, 5] p LIST`
	`INCREMENT = 1`
Contrary to variables, constants traverse method scopes.	`def incr(i) i + INCREMENT end`
	`p incr(5)`

$ ruby examples/constants/constants.rb
[1, 2]
[1, 2, 3]
examples/constants/constants.rb:18: warning: already initialized constant LIST
examples/constants/constants.rb:5: warning: previous definition of LIST was here
[4, 5]
6

Next example: Classes