From: "David A. Black" <dblack@...>
Date: 2005-08-08T10:45:28+09:00
Subject: Re: Adding yet another Array.new form

Hi --

On Mon, 8 Aug 2005, Kirk Haines wrote:

> On Sunday 07 August 2005 10:50 am, David A. Black wrote:
>
>>>> def a
>>>>   returning ary = [] do
>>>>     ... construct ary by adding elements to it ...
>>>>   end
>>>> end
>>
>> [...]
>>
>>> I'd rather vote in favor of including #returning to the Ruby core.
>>> It is a very helpful method to DRY.
>>
>> It feels a bit side-effect-dependent-ish, as written.  It might be
>> nicer with a more traditional yield/block param syntax:
>>
>>    returning [] do |ary| ... end
>>
>> That shows more of the separation between the fact that you're
>> returning an array, and the fact that you're assigning the name ary to
>> that array for use inside the block.
>
> It should work either way.  I haven't looked at the one in Rails, but mine:
>
> module Kernel
>        def returning(*vals)
>                yield *vals
>        end
> end
>
>
> def a
>  returning tmp = [] do
>    tmp << 1; tmp << 2; tmp << 3
>  end
> end

That only works by coincidence: tmp << 3 happens to return tmp :-)  If
anything else is the last expression in your block, you'll get a
different result:

   def a
     returning tmp = [] do
       tmp << 1; tmp << 2; tmp << 3
       puts "I've finished inserting into tmp!"
     end
   end

   a   # => nil, because it returns the value of the puts statement

#returning has to explicitly return the thing it yields; otherwise it
will return whatever the block it yielded to returns.


David

-- 
David A. Black
dblack@wobblini.net