What is the difference between a constant and a variable in Ruby?

Question

So, I\'m doing a Ruby course on CodeAcademy and I\'m stuck in differentiating the difference between a variable and a class. Can someone please explain the difference to me?

Answer 1

In Ruby, a constant is an identifier that starts with a capital letter; it is intended to be assigned only once. You can reassign a constant, but you should not. Doing so will generate a warning:

NAME = "Fred"
NAME = "Barney"    # => Warning: Already initialized constant NAME

A variable is an identifier that does not start with a capital letter; it may be assigned to more than once:

name = "Fred"
name = "Barney"    # => No warning

When you create a class, a constant is created with the same name as the class; that constant is bound to the class:

class Foo
end

This is equivalent to this code which creates a new anonymous class and assigns it to the constant Foo:

Foo = Class.new do
end

You can reassign the constant identifier Foo, as you can with any other constant, but of course you shouldn't, and you will still get the warning:

Foo = 123    # => Already initialized constant Foo