From: Mauricio Fernandez <mfp@...>
Date: 2007-01-08T23:44:19+09:00
Subject: Re: a most undangerous Hash#store!

On Mon, Jan 08, 2007 at 09:37:05PM +0900, dblack@wobblini.net wrote:
> On Mon, 8 Jan 2007, Mauricio Fernandez wrote:
> >On Mon, Jan 08, 2007 at 08:20:05PM +0900, Robert Klemme wrote:
> >>But only if you need the return value:
> >>
> >>irb(main):001:0> hash={:key=>1}
> >>=> {:key=>1}
> >>irb(main):002:0> hash.merge( :key => "new value" )
> >>=> {:key=>"new value"}
> >>irb(main):003:0> hash
> >>=> {:key=>1}
> >>
> >>The hash is merged properly.
> >
> >The original hash is not modified by #merge.
> >#merge != #merge! (== #update)
> >
> >a = {}
> >a.merge(:foo => 1)        # => {:foo=>1}
> >a                         # => {}
> 
> Yes, merge was just a wrong turn on my part.  Forget it.

To be fair, the reference to #merge was not entirely misguided, since

a = {:bar => 1, :foo => 2}
{:foo => 0}.merge(a)      # => {:bar=>1, :foo=>2}
{:baz => 0}.merge(a)      # => {:baz=>0, :bar=>1, :foo=>2}

It just happens to work the other way around (cf. #reverse_merge mentioned
earlier in this thread).

Anyway, Trans was talking about destructive updates, so what about

  def store?(key, value)                      
    unless key?(key)    
      store(key,value)
      return true
    end
    false
  end

similar to the #store! he described, but with a more regular behavior when you
have nil/false values...

-- 
Mauricio Fernandez  -   http://eigenclass.org   -  singular Ruby