How to determine if optional arguments are passed in Ruby

Question

If I have the following method in Ruby:

def foo(arg1, arg2 = "bar")
  puts arg1
  puts arg2
end

Is there a way of determining if a user passed a value in for arg2 within the method? Obviously I could just add if arg2 == "bar" to the method, but this doesn't catch the case where the user manually passed in "bar" herself. Of course, I could set the default to be something that no user would ever pass in, but then that gets pretty ugly pretty quickly.

Is there anything elegant out there?

Answer 1

def foo(arg1, arg2 = (arg2_not_passed = true; "bar"))
  puts arg1
  puts arg2
  puts 'arg2 was passed' unless arg2_not_passed
end

Answer 2

def foo(*args)
  case args.length
  when 1
    # arg2 was not given
    arg1, arg2 = args.first, "bar"
    ...
  when 2
    # arg2 was given
    arg1, arg2 = args
    ...
  else
    raise ArgumentError
  end
end