From: Bertram Scharpf <lists@...>
Date: 2010-01-02T22:48:11+09:00
Subject: Re: can't understand for this each

Hi,

Am Samstag, 02. Jan 2010, 21:20:02 +0900 schrieb Ruby Newbee:
> what's each{ .. } in the find_all method?
> 
> class Hash
>   def find_all
>     new_hash = Hash.new
>     each { |k,v| new_hash[k] = v if yield(k, v) }
>     new_hash
>   end
> end

`Hash#each' is not `Array#each'. It is descibed in
<http://www.ruby-doc.org/docs/ProgrammingRuby/html/ref_c_hash.html#Hash.each>.

It does something like 

  class Hash
    def each
      keys.each { |k|
        yield k, self[ k]
      }
    end
  end

A remarkable aspect is that `Hash#each' yields two values so that
everywhere in Enumerable's descriptions "{ |obj| ... }" has to be
replaced with "{ |k,v| ... }" or even "|(k,v)|". For example, you
have to call

  hash.each_with_index { |(k,v),i| ... }

Bertram


-- 
Bertram Scharpf
Stuttgart, Deutschland/Germany
*
Support `String#notempty?': <http://raa.ruby-lang.org/project/step>.