From: Rick DeNatale <rick.denatale@...>
Date: 2007-11-11T23:50:03+09:00
Subject: Re: equivalent injecting implementations?

On Nov 10, 2007 4:23 PM, Ezra Zygmuntowicz <ezmobius@gmail.com> wrote:
>
>
> On Nov 10, 2007, at 7:50 AM, Rick DeNatale wrote:

> > 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.
>
>
> injecting is similar to returning in rails.

>There is a common pattern
> of accumulating a hash via inject that looks like this:
>
> [1,2,3].inject({}) { |memo,n| memo[n] = n ;  memo}
> #=> {1=>1, 3=>3,2=>2}
>
> Note the ugly trailing ;memo, this is so the fll accumulated hash is
> the final return result.
>
> injecting is just a little bit nicer way to do the same thing:
>
> [1,2,3].injecting({}) { |memo,n| memo[n] = n }
> #=> {1=>1, 3=>3,2=>2}

Yes, I suspected that this was what Trans was trying to do, but since
the second proposed 'maybe equivalent' implementation didn't seem to
be doing the same thing, I was probing for what he really wanted.

Having said that, and played a bit with the concept. I'm not sure how
useful an injecting method (at least with that name is).

As Robert Klemme points out, it breaks depending on what you are
injecting. And it's subject to "cargo culting."

module Enumerable
  def injecting(obj, &blk)
    inject(obj) { |mem, var| yield(mem, var); mem }
  end
end

As Ezra points out:

[1,2,3].inject({}) { |memo,n| memo[n] = n ;  memo} # => {1=>1, 2=>2, 3=>3}
[1,2,3].injecting({}) { |memo,n| memo[n] = n}      # => {1=>1, 2=>2, 3=>3}

But this only works because the block has a side-effect on the memo
object.  And yes, in cases like this each instead of inject will have
the same side effects.

[1,2,3].inject(0) { |memo,n| memo + n}             # => 6
[1,2,3].injecting(0) { |memo,n| memo + n}          # => 0

Here's where the cargo cult danger comes in. Someone who comes across
'injecting' without understanding it might run into things like this.

So while the idea of an injecting method seems nice, I'm not enamored
of the name.

-- 
Rick DeNatale

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