Ruby optional arguments can come before required

I'm used to seeing optional arguments after required ones, as so:

require 'date'

def age(date, today=Date.today)
  (today - date) / 365.25 # good enough
end

birthdate = Date.parse("2011-06-15")

# How old am I today?
age(birthdate) #=> 4.583

# How old was I on the first?
age(birthdate, Date.parse("2016-01-01")) #=> 4.547

The second argument is optional.

However, you can also make the first argument optional:

def age(today=Date.today, date)
  (today - date) / 365.25 # good enough
end

birthdate = Date.parse("2011-06-15")

# How old am I today?
age(birthdate) #=> 4.583

# How old was I on the first?
age(Date.parse("2016-01-01"), birthdate) #=> 4.547

I don't recommend doing this. It's confusing.