From: Nikolai Weibull <now@...>
Date: 2011-10-14T19:49:11+09:00
Subject: What’s the best way of checking if an argument has been given or not?

Hi!

What’s the best way of checking if an argument has been given or not?

That is, what’s the best way of achieving

class A
  ArgumentMissing = Object.new.freeze

  def b(c = ArgumentMissing)
    if ArgumentMissing.equal? c
      puts 'no argument was given'
    else
      puts c
    end
  end
end

A.new.b # => no argument was given
A.new.b 1 # => 1

?  I remember seeing something that didn’t require a constant like
this, but I can’t seem to find it.  (Note: I don’t want to use nil for
this particular case.  I would preferably use a value that is
inaccessible outside of A.)