From: Nikolai Weibull <now@...>
Date: 2011-10-15T01:11:00+09:00
Subject: Re: What’s the best way of checking if an argument has been given or not?

On Fri, Oct 14, 2011 at 17:31, Jens Wille <jens.wille@uni-koeln.de> wrote:

> class A
>
>  def b(c = d = true)  # or some other truthy value
>    if d
>      puts 'no argument was given'
>    else
>      puts c
>    end
>  end
>
> end
>
> can't remember where i first saw it, but it works perfectly ;)

Yes, of course!  That’s the trick I saw too; checking if the optional
argument’s default value was evaluated.

Here’s a more general solution that allows you to set d to a value
independent of the desired default value for the argument:

def m(a = (d = true; nil))
  # d will be true if argument a wasn’t specified
end

One easily forgets how expressive Ruby can be.  Or how easily it is to abuse it.

Thanks!