From: Glenn Parker <glenn.parker@...>
Date: 2004-12-08T23:25:10+09:00
Subject: Re: Idiom for creating hash from two arrays

David A. Black wrote:
> On Wed, 8 Dec 2004, Glenn Parker wrote:
>> 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.
> 
> What if you wanted to set a default value for the hash?

Hash.new is already varadic:

      Hash.new                          => hash
      Hash.new(obj)                     => aHash
      Hash.new {|hash, key| block }     => aHash

The second form specifies a default value.  The third form specifies a 
block to generate missing values.  I was suggesting that we add one more 
form:

      Hash.new(keyArray, valueArray)    => aHash

This form is easily distinguishable from the original three, so you 
could still create a hash with a default value using the second or third 
form.

However, the more I think about it, the more I see this as a typical 
operation on existing hashes, not simply a constructor.  So, I would 
rather see alternate forms for merge and update:

      Hash#merge(keyArray, valueArray)
      Hash#update(keyArray, valueArray)

Then, to the original problem would be expressed as:

      h = Hash.new.merge(keyArray, valueArray)

-- 
Glenn Parker | glenn.parker-AT-comcast.net | <http://www.tetrafoil.com/>