From: "David A. Black" <dblack@...>
Date: 2009-01-05T06:22:37+09:00
Subject: Re: Default values of hashes

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Hi --

On Mon, 5 Jan 2009, Sebastian Hungerecker wrote:

> Glenn wrote:
>> In other words, if I need 3 levels, it creates a hash within hash object=
 3
>> levels deep (like in the line of code above) and if I need 5, it creates
>> one 5 levels deep. =A0I do not know how to do this (or even if it is
>> possible). =A0Any suggestions on this one?
>
> def nested_hash(levels, def_value=3Dnil, &def_proc)
>  inner_hash =3D def_proc ? Hash.new(&def_proc) : Hash.new(def_value)
>  if levels =3D=3D 1
>    inner_hash
>  else
>    l =3D [lambda {|h,k| h[k] =3D inner_hash}]
>    (levels-2).times do |i|
>      l[i+1] =3D lambda {|h,k| h[k] =3D Hash.new( &l[i] ) }
>    end
>    Hash.new(&l[-1])
>  end
> end
>
> This creates a nested hash levels levels deep, where the innermost hash c=
an
> optionally have a default value or proc.
>
> Usage:
> h =3D nested_hash(1)
> # Same as h =3D Hash.new
>
> h =3D nested_hash(1) {|h,k| h[k] =3D Array.new}
> # Same as h =3D Hash.new {|h,k| h[k] =3D Array.new}
>
> h =3D nested_hash(3)
> # Same as h =3D Hash.new {|h,k| h[k] =3D Hash.new {|h,k| h[k] =3D Hash.ne=
w}}
>
> h =3D nested_hash(3, :foo)
> # Same as h =3D Hash.new {|h,k| h[k] =3D Hash.new {|h,k| h[k] =3D Hash.ne=
w(:foo)}}

Why not make it just keep going automatically? (See my other post.)


David

--=20
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
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