From: Rob Biedenharn <Rob@...>
Date: 2008-08-19T00:38:57+09:00
Subject: Re: Hash#each vs Hash#each_pair


On Aug 18, 2008, at 9:56 AM, Patrick Doyle wrote:

>> p "p hash : #{hash}"
>> p "hash.each"
>> hash.each do |e| #e is [key,value]
>> p e
>> end
> I am just trying to understand why hash.each returns [key, value]
> instead of value the way that array.each does:
> #!/usr/bin/ruby
>
> hash = {1 => 'one', 2 => 'two', 3 => 'three'}
> array = ['one', 'two', 'three']
>
> p "p hash : #{hash}"
> p "hash.each"
> hash.each do |e| #e is [key,value]
> p e
> end
>
> p "p array : #{array}"
> p "array.each"
> array.each do |e|
> p e
> end
>
> The answer might be "because that's the way it's always been done, and
> there's no way we're going to change it because a newbie asked for it
> to be changed!".  (The careful reader might notice that I haven't
> asked for anything to be changed -- I'm simply trying to understand
> the thinking that went into the decision to make Hash#each operate
> differently than Array#each)
>
> In my case, I have some code in which a bunch of data has been
> collected into an array, and I would like to modify my code such that
> the collection of data is stored in a Hash instead of an Array object.
> I had assumed that, since I used object.each everywhere that I
> iterated through my data, it would be as simple as changing the code
> where I stuff the values into the collection.  Obviously, my
> assumption proved incorrect.  Which led me to the question, "Now, I
> wonder why they did that?"  So I've asked the question.
>
> --wpd
>
(It seems that my first response got swallowed by the web)

An Array contains elements, a Hash contains key-value pairs.  Doesn't  
that make sense that Hash#each returns the pairs?  It seems that your  
mental picture of "values of the container" is at odds with Ruby (Matz).

You could alias Array#each_value to be Array#each and then use  
each_value for both types.

Perhaps if your motivation for changing from Array to Hash was  
eliminating duplication, you really want to use a Set
-Rob
Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
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Skype:	rob.biedenharn