ruby code: why put colon in front of variable name (inside initialize method)

Question

I came across some Ruby code, I try to understand why the variables have colon at the end of their name inside the declaration of the initialize method.

Is there any reason for the colon?

attr_reader :var1, :var2

def initialize(var1:, var2:)
   @var1 = var1
   @var2 = var2
end

Answer 1

Those are keyword arguments.

You can use them by name and not position. E.g.

ThatClass.new(var1: 42, var2: "foo")

or

ThatClass.new(var2: "foo", var1: 42)

An article about keyword arguments by thoughtbot