From: Chris Shea <cmshea@...>
Date: 2009-08-20T05:40:07+09:00
Subject: Re: #has_arguments?

On Aug 18, 11:37 pm, Intransition <transf...@gmail.com> wrote:
> Messing with optional argument check for the umpteenth time, eg.
>
>   def meth(a=Exception)
>     if a != Exception
>        ...
>     else
>       ...
>     end
>   end
>
> Other's might do:
>
>   def meth(*a)
>     if !a.empty?
>       a = a.first
>        ...
>     else
>       ...
>     end
>   end
>
> Neither of which are very satisfying. So it occurs to me tonight that
> we already have #has_block? to see if a block was passed. So how about
> a #has_arguments? to query if _any_ arguments have been passed. So
> then...
>
>   def meth(a=default)
>     if has_arguments?
>        ...
>     else
>       ...
>     end
>   end
>
> Ah... now that would be nice.

Here's a little trick I learned (very hacky):

  def meth(a=(no_argument='default'))
    if no_argument
      'nothing given'
    else
      "we got #{a.inspect}"
    end
  end

Your default argument can't be falsy (but you could use something
truey and use your falsy value in its place).  Anyway:

  036:0> meth
  "nothing given"
  037:0> meth(nil)
  "we got nil"
  038:0> meth('whatever')
  "we got "whatever""
  039:0> meth
  "nothing given"

I can't vouch for JRuby or Ruby 1.9 or Rubinius or IronRuby for this
one (work's a strictly 1.8.6 kind of place).

-Chris