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From: Joel VanderWerf <joelvanderwerf@gmail.com>
Newsgroups: comp.lang.ruby
Subject: Re: Initialize Struct from Hash
Date: Fri, 29 Apr 2011 10:27:49 -0500
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.ruby:3702

On 04/29/2011 01:06 AM, Robert Klemme wrote:
> 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

That's intended: #structify is supposed to turn a hash into something 
that looks like a Struct, not an OpenStruct.