From: Rick DeNatale <rick.denatale@...>
Date: 2007-11-11T00:50:27+09:00
Subject: Re: equivalent injecting implementations?

On Nov 10, 2007 9:37 AM, Trans <transfire@gmail.com> wrote:
>
>
> On Nov 10, 8:50 am, "Rick DeNatale" <rick.denat...@gmail.com> wrote:
> > On 11/9/07, Trans <transf...@gmail.com> wrote:
> >
> >
> >
> > > Are these strictly equivalent? I get the feeling no, but I haven't
> > > been able to demonstrate it yet.
> >
> > >   def injecting(s)
> > >     inject(s) do |k, i|
> > >       yield(k, i); k
> > >     end
> > >   end
> >
> > >   def injecting(res, &block)
> > >     ([res]*length).zip(to_a).each(&block)
> > >     res
> > >   end
> >
> > > Thanks,
> > > T.
> >
> > I can't see how in general they can be.
> >
> > In which class or module are you defining these?  Since you are using
> > inject and each, I'm guessing that it's either Enumerable or some
> > subclass,
> >
> > But then depending on which subclass you don't have a length method so...
> >
> > Perhaps some more context would help.
>
> Oh sorry, I meant to put that. These are Enumerable methods.
>
module Enumerable
  def injecting(s)
     inject(s) do |k, i|
       yield(k, i); k
     end
   end

   def injecting2(res, &block)
     ([res]*length).zip(to_a).each(&block)
     res
   end
 end

(1..3).injecting(0) {|k,i| k + i} # => 0
(1..3).injecting2(0) {|k,i| k + i} # =>
# ~> -:9:in `injecting2': undefined local variable or method `length'
for 1..3:Range (NameError)
# ~> 	from -:15

Which illustrates my point.

Just what is injecting supposed to mean anyway? The first
implementation uses inject and takes a two argument block like inject
does, but seems to be going out of it's way to disregard the value of
the argument block.

This doesn't seem much like inject to me.



-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/