From: nobu.nokada@...
Date: 2002-12-19T10:28:18+09:00
Subject: Re: Hash.new{...} bug?

Hi,

At Wed, 18 Dec 2002 22:54:59 +0900,
Bulat Ziganshin wrote:
> >> hash = Hash.new{Hash.new}
> nnsn> Hash 'default' proc never modify the hash itself automatically.
> nnsn> Try with this.
> 
> nnsn>   hash = Hash.new {|h,k| h[k] = Hash.new}
> 
> thanks. but with Hash.new(...) hash element updated to default value.
> is this difference intended?

In the first style you wrote, the returned value is updated but
discarded soon.  The last style, the default value is updated
as same but kept in the hash and reused.

`Default value' may need operator assignments to work well.

  h = Hash.new(0)
  h[0] += 1
  h[:foo] += 2
  p h			# {0=>1, :foo=>2}

  class Hash
    def <<(arg)
      if Hash === arg
        update(arg)
      else
        store(*arg)
      end
      self
    end
  end
  h = Hash.new {{}}
  h[:foo] <<= [:bar, 1]
  h[:zot] <<= {:baz=>2}
  p h			# {:zot=>{:baz=>2}, :foo=>{:bar=>1}}

-- 
Nobu Nakada