From: Robert Klemme <bob.news@...>
Date: 2004-07-12T17:57:24+09:00
Subject: Re: Ruby quickies and useful idioms


"Sam Stephenson" <sstephenson@gmail.com> schrieb im Newsbeitrag
news:11fb0551040711161466c5309f@mail.gmail.com...
> On Mon, 12 Jul 2004 07:47:12 +0900, Gavin Sinclair
> <gsinclair@soyabean.com.au> wrote:
> > 'foldl' is, I believe, the same as Enumeration#inject.  Try checking
> > out the docs for that, but:
> >
> >   (1..100).inject(0) { |acc,x| acc + x }
>
> Wow, I didn't know about Enumerable#inject. Semantically, it's not
> quite the same as foldl: for instance, it doesn't make sense to foldl
> (or foldr) a Hash, since you're not guaranteed any order.

That's not true.  Since + is commutative it doesn't matter in which order
you add elements up.  And there's a whole lot other algorithms that don't
depend on the order in which they are processed.

Even if you need an order you can do (stupid example):

sorted_keys = hash.sort.inject([]) {|keys, (key, val)| print key, " -> ",
val, "\n"; keys << key }

> Practically
> speaking, however, it's much nicer, since I can use it with Range.
>
> As an aside: It would be nice to have a subclass of Enumerable that
> guarantees item order; Array, Range, et al could mix it in.

Which order?  Insertion order, natural order of the elements or an
arbitrary order?

Regards

    robert