From: Rick DeNatale <rick.denatale@...>
Date: 2009-03-30T01:54:53+09:00
Subject: Re: Is there an idiom for mass-populating Hash keys?

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On Sun, Mar 29, 2009 at 12:05 PM, Shot (Piotr Szotkowski) <shot@hot.pl>wrot=
e:

> Hello, good folk of ruby-talk.
>
> I was wondering whether there=92s a Ruby
> idiom to mass-populate keys of a Hash.
>
> I=92m coding a graph class supporting labeled vertices, and I want to
> represent this relationship as a @vertices Hash, with keys being the
> actual vertices and values being their labels =96 initially all nil:
>
> class Graph
>  def initialize enum
>    @vertices =3D {}
>    enum.each { |vertex| @vertices[vertex] =3D nil }
>  end
> end
>
> Is there a more elegant way to take an enum
> and turn it into nil-referencing Hash keys?
>

Why bother?  The only reason I can thing of is that you want to use
@vertices.keys to get the collection of vertices, but why be indirect.

class Graph
  def initialize(enum)
     @vertices =3D enum
     @labels =3D {}
  end
end

@labels[anything] will return nil if anything isn't a key.


--=20
Rick DeNatale

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