From: Robert Klemme <shortcutter@...>
Date: 2011-04-29T17:06:42+09:00
Subject: Re: Initialize Struct from Hash

On Thu, Apr 28, 2011 at 10:50 PM, Joel VanderWerf
<joelvanderwerf@gmail.com> wrote:

> Tangentially, I wonder if anything like the following (very rough proof of
> concept) has been used instead of Struct.
>
> class Hash
>  def structify!
>    keys.each do |key|
>      class << self; self; end.class_eval do
>        define_method key do
>          fetch key
>        end
>        define_method "#{key}=" do |val|
>          store key, val
>        end
>      end
>    end
>  end
> end
>
> h = {:foo => 1, :bar => 2}
> h.structify!
> p h.foo # 1
> h.foo = 3
> p h.foo # 3
> p h     # {:foo=>3, :bar=>2}
> p h.oof # undefined

irb(main):004:0> h = {:foo => 1, :bar => 2}
=> {:foo=>1, :bar=>2}
irb(main):005:0> o = OpenStruct.new(h)
=> #<OpenStruct foo=1, bar=2>
irb(main):006:0> o.foo
=> 1
irb(main):007:0> o.bar
=> 2

Well, here we differ

irb(main):008:0> o.oof
=> nil

But the issue with your approach is that it is not dynamic.  Keys
added or removed after call to #structify! will not be taken care of.
A more dynamic approach would be

module HashStruct
  def method_missing(s,*a,&b)
    case
    when a.empty? && key?(s)
      self[s]
    when a.size == 1 && /\A(.+)=\z/ =~ s
      self[$1.to_sym] = a.first
    else
      super
    end
  end
end

h.extend HashStruct
h.foo

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/