From: Todd Benson <caduceass@...>
Date: 2008-02-09T14:29:16+09:00
Subject: Re: info on block arguments

On Feb 6, 2008 8:25 PM, Russell Me <russ@geekwhiz.com> wrote:
> I'm trying to pick up ruby and I'm impressed by all the cool stuff it
> does out of the box. I'm reading a few books but i'm finding why's
> poignant guide to ruby to be the most helpful and entertaining
> (http://poignantguide.net/ruby).
>
> However, I'm a bit stuck understanding how block arguments work. in his
> example:
>
> kitty_toys = [
>    {:shape => 'sock', :fabric => 'cashmere'},
>    {:shape => 'mouse', :fabric => 'calico'},
>    {:shape => 'eggroll', :fabric => 'chenille'}
>  ]
>
> kitty_toys.sort_by { |toy| toy[:shape] }.each do |toy|
>    puts "Blixy has a #{ toy[:shape] } made of #{ toy[:fabric] }"
>  end
>
> I know what it does. I put it through irb and it works. But i don't
> understand HOW it works, exactly. Mainly, the toy bit. I don't quite get
> what role it plays in the code and how the code uses it.
>
> I've read up online and in both books I have, but, for whatever reason i
> STILL cannot grasp block arguments and what role they play.
>
> Maybe I'm just brain farting here, but if anyone could lend some tips on
> this I'd appreciate it.

As others have pointed out, the #sort_by method _throws_ you a
reference (doesn't have to be called "toy") and you do whatever you
want with it.  What your block _should_ do largely depends upon how
the calling method works.

In this case, #sort_by throws your block object references (one at a
time) and you are supposed to give it back an object reference that is
comparable (i.e. responds to the <=> method).

At least, that's the way I understand it without reading the underlying code.

A _very_ simple example...

def simple
  yield 3
end

simple {|i| puts i}


Todd