From: Bruce Woodward <bruce.woodward@...>
Date: 2006-04-13T21:14:12+09:00
Subject: Re: map_if, collect_if ???

------=_Part_18803_17340494.1144930447706
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

Robert and Logan,

Thanks for your replies. That was good thinking.

On 4/13/06, Robert Dober <robert.dober@gmail.com> wrote:
>
> On 4/13/06, Bruce Woodward <bruce.woodward@gmail.com> wrote:
>
> module Enumerable
>     def map_if( &block )
>         find_all(&block).map(&block)
>     end
> end


I particularly like the use of calling block twice. At first I thought that
this couldn't work but of course once the block has been successful for the
call to find_all, it must be successful for the call to map -- very nice.

I will file away the find_all  {}.map {} idiom for future use but for this
case I will either use a manual accumulator or inject. The only reason is
performance and performance only matters in this case because the code is
likely to be get call many hundreds of times in a loop and I will be
impatiently waiting for it finish.

WRT to performance, not only is the block being called twice but an extra
array is being created and then freed. In the past I have had issues ruby
processes using a lot of memory and spending time with the garbage
collector. I don't want to start any kind of anti-ruby flame war here;  Rub=
y
is my first choice. Manually stopping the GC at the top of the loop and
starting the GC at the bottom of the loop, solved the problem but I just
want to minimse memory use where I can, just for this code.

thanks again.
Bruce.

------=_Part_18803_17340494.1144930447706--