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List:       ruby-talk
Subject:    Re: Underscore
From:       Robert Klemme <shortcutter () googlemail ! com>
Date:       2007-05-31 11:10:16
Message-ID: 5c7oiuF2vca0oU1 () mid ! individual ! net
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On 31.05.2007 11:51, Robert Dober wrote:
> On 5/31/07, Robert Klemme <shortcutter@googlemail.com> wrote:
>> On 30.05.2007 22:36, Robert Dober wrote:
>> > On 5/30/07, Logan Capaldo <logancapaldo@gmail.com> wrote:
>> >> On 5/30/07, Robert Dober <robert.dober@gmail.com> wrote:
>> >> >
>> >> > On 5/30/07, Brian Candler <B.Candler@pobox.com> wrote:
>> >> > > On Wed, May 30, 2007 at 07:50:05AM +0900, Logan Capaldo wrote:
>> >> > > > On 5/29/07, Robert Klemme <shortcutter@googlemail.com> wrote:
>> >> > > > >
>> >> > > > >
>> >> > > > >I was too fast (again).  Even though the return value is 
>> used, I'd
>> >> > rather
>> >> > > > >do
>> >> > > > >
>> >> > > > >n.times { x = yield x }
>> >> > > > >
>> >> > > > >than using #inject which does more than needed in this 
>> case.  :-)
>> >> > > > >
>> >> > > > >Now, did I look at all aspects...?
>> >> > > >
>> >> > > >
>> >> > > > Almost.
>> >> > > > you'd actually need
>> >> > > > n.times { x = yield x }
>> >> > > > x
>> >> > >
>> >> > > Almost almost :-)
>> >> > >
>> >> > > x = nil
>> >> > > n.times { x = yield x }
>> >> > > x
>> >> > >
>> >> > >
>> >> > Robert was very quick indeed, he did not repeat the context of the
>> >> > expression which was
>> >> >
>> >> > def forgot_the_name(x,...)
>> >> >     n.times{ x = yield x }
>> >>
>> >>
>> >>       Still need x here
>> >>
>> >> end
>> >> >
>> >> > Now it works ;)
>> >>
>> >>
>> >> No it doesn't ;)  n.times {  ... } returns n.
>> > Obviously I am too stupid to test, sorry, I did test it, who knows 
>> how ;)
>> > Seriously I do know now, n just was the expected result of the block :(
>> >
>> > def anyhow(count, x)
>> >  count.times{x=yield x}
>> >  x
>> > end
>> >
>> > Maybe we can still agree that this is better than inspect ;)
>> > And yes thanks for the Ruby classes I got.
>>
>> Hm...  Thinking a bit more about this I am not sure I'd stick with my
>> proposal.  I think I'd probably do
>>
>> irb(main):001:0> require 'enumerator'
>> => true
>> irb(main):002:0> def rep(n,init=nil) n.to_enum(:times).inject(init)
>> {|x,| yield x} end
>> => nil
>> irb(main):003:0> rep(5,"x") {|s| puts s; s<<"."}
>> x
>> x.
>> x..
>> x...
>> x....
>> => "x....."
>>
>> Hmm...
> As we are fooling around ;)
> 
> class Integer
>  alias_method :good_old_times, :times
>  def times
>    r = nil
>    good_old_times do
>      |n|
>      r = Proc.new.call n
>    end
>    r
>  end

You are aware that this does something different, especially will it 
return the last block value only.

Also, why do you use Proc.new.call instead of yield?

>  def rep init = nil
>    times do
>       init = Proc.new.call init
>    end
>  end
> end
> 
> 
> puts 5.times{ |x| 2*x }
> puts 5.rep(12){ |x| x+1 }
> BTW what is this good for anyway ;) for loops???

Probably.  I tend to believe that usually #inject is better for 
calculations that involve repetition and want to process the result of 
the last calculation.  Usually I don't think that the iteration value is 
ignored in such cases.  Maybe the OP had a specific example in mind.

The initial question was what does the underscore do in

def nest(x, n = 2)
   (1..n).inject(x) { |acc, _| yield(acc) }
end

Basically it's completely superfluous, you can do this instead:

def nest(x, n = 2)
   (1..n).inject(x) { |acc,| yield acc }
end

Btw, I'd rather change the argument handling because n=2 is a pretty 
arbitrary default.

def nest(n, x = nil)
   (1..n).inject(x) { |acc,| yield acc }
end

Kind regards

	robert

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