From: James Coglan <jcoglan@...>
Date: 2008-07-23T19:23:41+09:00
Subject: Re: Generate accessors for an hash

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>
> I tried this code in the class constructor:
>
>    for a in all_attributes
>      method_name = a.name
>      self.class.class_eval do
>        define_method method_name do
>          @attributes[method_name]
>        end
>        define_method method_name+"=" do |val|
>          @attributes[method_name] = val
>        end
>      end
>    end
>
> It generates the method for the class, but all the methods read and
> write to the last attribute in the all_attributes list. That's
> strange...



Ah, the strange joy that is closures. Basically, those 'define_method' calls
allow the code block to retain access to whatever variables were in scope
when the methods are defined. So, when those methods actually run, the
variable 'method_name' will have the last value in the loop -- each closure
references a single variable, it does not copy its value.

You might be better off with method_missing

class Hash
  def method_missing(name, value = nil)
    name = name.to_s
    if name =~ /=$/
      self[name.sub(/=$/, '')] = value
    else
      return self[name]
    end
  end
end

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