subclassing doesn't work

[chuckremes]

See this gist for the same error under both rubinius and mri 1.9.2:

https://gist.github.com/1079682

Here is my use-case. I send hashes over the network to communicate amongst distributed processes. The hash oftentimes look like so:

message = {
'code' => 3,
'operation' => 'create',
'payload' => {
'field1' => [1,2,3],
'field2' => 'string',
'field3' => 5
}
}

I would like to be able to pass that entire hash to a ClassyStruct and conditionally have only the payload get parsed. When accessing 'field1' and others, I don't want to do foo.payload.field1 (I throw away 'code' and 'operation'). I want to reach them directly like foo.field1.

So I write code like:

MessageParent = ClassyStruct.new

class Message < MessageParent
def initialize(document = nil)
if document
if document.has_key?('payload')
super(document['payload'])
else
super(document)
end
else
super()
end
end
end

This allows me to pass a one-level hash to Message and have it parsed the way I like it. The initializer also let's me pass a hash with an embedded payload and parse it the way I like it. Lastly, I can pass nothing/nil and set the fields manually.

Unfortunately, subclassing a ClassyStruct blows up. :(

Is there a work around or a fix?

[chuckremes]

BTW, I really appreciate ClassyStruct. Performance-wise it BLOWS AWAY the OpenStruct class. It is also much more intelligent about parsing nested structures. Subclassing (so I can customize the initializer) would be so nice...

[chuckremes]

After a little research this morning, I see that it's due to class instance variables not being inheritable. Here's an explanation that made sense to me:

http://stackoverflow.com/questions/2752641/ruby-class-instance-variables-and-inheritance

I don't have a fix yet. Whenever I get into metaprogramming my head starts to spin. :)

[chuckremes]

Here is a workaround using the 'delegate' functionality from stdlib.

require 'rubygems'
require 'classy_struct'
require 'delegate'

message = {
  :code => 3,
  :operation => 'create',
  :payload => {
    :field1 => 'string',
    :field2 => [1,2,3,5],
    :field3 => 9
  }
}

A = ClassyStruct.new

class B < DelegateClass(A)
  def initialize(hash = nil)
    if hash
      if hash.has_key?(:payload)
        puts "b1"
        super(hash[:payload])
      else
        puts "b2"
        super(hash)
      end
    else
      puts "b3"
      super(A.new)
    end
  end
end

# first branch of if/else
b1 = B.new(message)
p b1

b2 = B.new(message[:payload])
p b2

b3 = B.new
b3.field1 = 4
p b3

This outputs what I expect.

b1
{:field2=>[1, 2, 3, 5], :field1=>"string", :field3=>9}
b2
{:field2=>[1, 2, 3, 5], :field1=>"string", :field3=>9}
b3
{:field1=>4}

[chuckremes]

Alas, I spoke too soon. While the object appears to be populated correctly, it is not possible to access the fields. The delegator is also using #method_missing, so what happens is the ClassyStructClass#method_missing receives a call with name = :method_missing and the *args= [:field1].

Oh well... I've run out of gas on this one.