From: David Alan Black <dblack@...>
Date: 2002-02-25T11:22:16+09:00
Subject: Re: Hash.each block parameters

Hi --

On Mon, 25 Feb 2002, Sean O'Dell wrote:

> I ran into a problem where I should have called .each_key for a hash, but I
> was calling .each and so I wrote it like this:
>
> myhash.each do | key |
> end
>
> I couldn't get values out of the hash using the key during the block
> iterations.  nil was always returned.
>
> I studied my code awhile and realized I should be using each_key.  Hash.each
> provides TWO block parameters, not one like each_key (the key).  I added the
> second parameter and things were fine again.
>
> It did this very quietly, no error or anything...I just got nil values and
> scratched my head until I figured it out.  Is there a parameter to make Ruby
> stricter towards this sort of thing?

Ruby isn't doing anything it shouldn't :-)

When you iterate through a Hash with #each, you get each pair.  So
your variable "key" is actually an two-element array:

  myhash = Hash[*%w{ one un two deux three trois }]
  myhash.each {|pair|  puts "key: #{pair[0]}; value: #{pair[1]}" }

  =>
     key: three; value: trois
     key: one; value: un
     key: two; value: deux

Actually you could just capture the key by putting in a comma:

  myhash.each {|key,| ... }

but in this case it's clearer to use each_key, or myhash.keys.each .


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav