Alex Gutteridge wrote:
> The problem I have is that sometimes I have extra data associated with
> the Atom and/or Residue objects. This extra data always comes later
> (from a different data file) and usually won't be present. when I need
> to, I'd like to add this data to the (already created data structure)
> with the minimum amount of work/fuss.
> 
> As far as I can see I have the following options:
> 
> 1. Modify the Atom and Residue classes to include the extra data, set
> to nil originally and then filled in when needed. I'd rather not do
> this because the code is part of a bigger project which I don't have
> direct control over, and it seems rather inelegant to have these extra
> fields which hardly ever get used.
> 
> 2. Create a new AtomExtra class which inherits from Atom but adds
> instance variables and accessors for the new data. Then when I read
> the extra data I transform each Atom object into an AtomExtra object
> and add the new data. I guess the crux of my question is what's the
> neatest, Rubyist way of doing this: Is there a smart way of 'morphing'
> an object into another type of object (Atom to AtomExtra in this case)
> or do I have to create a new object, copy all the data across and then
> reattach the new object into the container structure.
> 
> Thanks in advance for any advice or help you can give!

# 3. Create a ExtraAtomFunctionality module that you
#    extend your Atom objects with dynamically.

class Atom
   #...
end

module ExtraAtomFunctionality
   attr_accessor :my_extra_stuff
end

a = Atom.new
# ...then later when you find you need to augment the object...
a.extend ExtraAtomFunctionality
a.my_extra_stuff = "Rogue electron"

# It may eat more memory than your other suggestions,
# since it would make singleton classes for each
# augmented Atom instance.

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