From: Robert Klemme <bob.news@...>
Date: 2004-04-24T18:24:06+09:00
Subject: Re: Array to Hash


"Mark Hubbart" <discord@mac.com> schrieb im Newsbeitrag
news:36BA84AE-95B4-11D8-9D1D-000502FDD5CC@mac.com...
>
> On Apr 23, 2004, at 10:14 PM, Ara.T.Howard wrote:
>
> > On Sat, 24 Apr 2004 nobu.nokada@softhome.net wrote:
> >
> >> Hi,
> >>
> >> At Sat, 24 Apr 2004 13:05:20 +0900,
> >> Pe�a, Botp wrote in [ruby-talk:98203]:
> >>> I would rather prefer:
> >>>
> >>>>> h2 = a.to_hash   # or a.to_h
> >>> {"x"=>1, "y"=>3}
> >>
> >> module Enumerable
> >>   def to_h
> >>     inject({}) {|h, (k, v)| h[k] = v; h}
> >                       ^^^^^^
> >                       ^^^^^^
> >                       ^^^^^^
> >                       what's this?
> >>   end
> >> end
>
> module Enumerable
>    def to_h
>      inject({}) {|h, (k, v)| h[k] = v; h}
>                   ^   ^^^^
>                   1     2
> 1: is the hash that keeps being passed through inject each time.
> 2: is the key=>value pair, expanding it from a two element array.
>
> I didn't even realize you could do that type of assignment in a block's
> parameter list, but hey! that's pretty cool.
>
> I think this should be a standard Array method. There have been many
> times I've done just this type of thing to get a hash from an array,
> for various reasons.

There's one reason why this may not be a standard method: there are at least
two equally reasonable representations of a mapping stored in an array:

Nested arrays as returned by Hash#to_a: [[key1, val1], [key2, val2]]

A sequence: [key1, val1, key2, val2] as used by Hash[]

Obviously there is no simple way from a Hash to an Array and back to a Hash.
(Btw: is that ever needed? I mean, if you have a hash you can easily create
a copy without an intermediate array.)

So the question is wich representation Enumerable#to_h should expect -
nested or sequence?

    robert