From: "David A. Black" <dblack@...>
Date: 2005-10-07T10:10:41+09:00
Subject: Re: select! not present but reject! is

Hi --

On Fri, 7 Oct 2005, Jacob Fugal wrote:

> On 10/6/05, David A. Black <dblack@wobblini.net> wrote:
>> ...
>>
>> In the middle of writing this I finally got a handle on what bothers
>> me about select! as (I think) it's being discussed: it's backwards.
>>
>> If you select! elements from an array (dangerous/destructive select),
>> those elements should be *removed* from the array.  It's like
>> selecting people from the audience to come onto the stage: they are
>> removed from the audience.  The audience is not reduced to being just
>> them.
>
> Hmm, I'd disagree. After all, we're sending the message to the array
> aren't we?

That's true across the board, though; it's not a determinant of what
happens when we send a message.

> I look at it like John the Innocent Array has five apples,
> two shiny and three dull. I come along, as the wise programmer, and
> say to Johnny, "Johnny, shiny apples are good. You only need to keep
> those ones." In Ruby:
>
>  johnny = []
>  2.times { johnny << ShinyApple.new }
>  3.times { johnny << DullApple.new }
>
>  # ... later ...
>
>  johnny.select! { |a| a.shiny? }

Or you could look at it as: "Give me (permanently) all your shiny
apples!"

   my_apples = johnny.select! {|a| a.shiny? }

So now my_apples has them, and johnny doesn't.  Mind you, I'm not
eager to see my version in the language either.  I don't like the bang
method not returning the receiver.  But I don't like the semantics, in
this case, when it does.  (And the find_all! thing is a further sign
that this method was not meant to have a bang version.)

I think there's been talk in the past of delete_unless.  delete_if is
not quite the same as reject! (one of them returns nil if nothing's
found; the other returns an array, I believe).


David

-- 
David A. Black
dblack@wobblini.net