From: Brian Mitchell <binary42@...>
Date: 2006-04-21T07:00:49+09:00
Subject: Re: Optional Message Parameters?

On 4/20/06, Nathan Olberding <nathan.olberding@gmail.com> wrote:
> (Warning: Newbie Altert!)
>
> How do I write a method with optional params? I would think that this:
>
> def do_this(opt1="", opt2="")
>         puts opt2
> end
> do_this(opt2="This")
>
>
> Would result in "This" being displayed. Instead, "This" becomes the
> value of opt1. I'd like to set opt1 and opt2 to default to "". How do I
> do that?

This is usually a case where you either use * or a hash parameter. *
is good for cases where you can distinguish by value. In your case it
looks like a hash would be appropriate.

def do_this(opts)
  puts opt[:two]
end

do_this(:two => "This")

Notes: The hash parameter will always be the last parameter (ignoring
& args and other odd parameter changes when using super). This means
you can pass many things along side the hash, though the more you add
the more complex it gets to manage the interface. Rails uses this
technique heavily. Have a look at the find() code in ActiveRecord
sometime to learn how they manage such an interface (much cleaner in
more recent releases).

Future major versions of Ruby are going to have actual named
parameters. So much to look forward to in 2.0!

Brian.