From: "David A. Black" <dblack@...>
Date: 2004-12-09T04:44:17+09:00
Subject: Re: Idiom for creating hash from two arrays

Hi --

On Thu, 9 Dec 2004, Glenn Parker wrote:

> David A. Black wrote:
>> On Thu, 9 Dec 2004, Glenn Parker wrote:
>>> This style of expression can only create a new hash instead of updating an 
>>> existing hash.  I think the "core" operation is updating/merging an 
>>> existing hash with a set of matched keys and values.
>> 
>> hash.update(key_array.hash_with(value_array)) :-)
>
> Unless Ruby is much smarter than I thought, this will build a new (albeit 
> temporary) hash, then pass it to Hash#update.  Not quite the same as updating 
> hash in place, and less efficient in terms of memory usage.
>
> The smiley suggests to me you already appreciate this distinction. :)

Not exactly... more that I don't think updating an existing hash from
two arrays really needs its own semantics, beyond those provided by
Hash#update.  I think the most common uses of Hash#update involve
hashes that already exist.  So, for example, you might have:

   hash.update(Hash[*some_array.flatten])

which also probably isn't the most efficient possible way, but I'd
rather keep the question of optimizing Hash#update separate from the
question of creating hashes out of two arrays.


David

-- 
David A. Black
dblack@wobblini.net