From: "trans.  (T. Onoma)" <transami@...>
Date: 2004-12-08T23:13:12+09:00
Subject: Re: Idiom for creating hash from two arrays

On Wednesday 08 December 2004 09:02 am, Jonathan Paisley wrote:
| On Wed, 08 Dec 2004 22:30:08 +0900, Glenn Parker wrote:
| > Jonathan Paisley wrote:
| >> Hash.zipnew ... I quite like the similarity to Hash.new, and the
| >> inclusion of the already familiar zip idea is also a good thing.
| >
| > Why does it need a new name?  Instead, why not extend Hash.new to do
| > this when it is passed two arrays?  It seems pretty natural to me, and I
| > don't see any conflict with existing usage.
|
| That's certainly a possibility. I suppose the disadvantage of this is that
| the semantics would then be quite different between one and two arguments:
|
|  1 argument  : specify the default value
|  2 arguments : populate the hash with pairings of keys and values
|
| I think it would be more natural to extend the existing Hash[] method, if
| that didn't cause a conflict with the existing usage. The question, then,
| is whether you'd ever want to construct a hash with just one entry, whose
| key and value are arrays.
|
|   h = Hash[keys,values]
|
| I suppose if you did want the one-entry-hash, you could always do:
|
|   h = Hash[key=>value]
| or even just
|   h = { key=>value }

How do you set the default value after the fact?

  h = {}
  h.default=x  #?

Personally I have never like how Hash.new works. I've always felt that #new 
for core classes should be able to take there selves:

  h1 = { :a=>1, :b=>2 }
  h2 = Hash.new(h1)

Default makes more sense as an option:

  h2 = Hash.new(h1, :default=>0)

Although that take away one somewhat useful construction patterns, namely

  h2 = Hash.new(:a=>1, :b=>2, :default=>0) #would not work

man, how cool might it be if Ruby had a secondary argument divider to group 
sets of parameters.

T.