From: Doug Glidden <41mortimer@...>
Date: 2008-08-24T10:09:52+09:00
Subject: Passing parameters into a singleton class def?

Hi,

I'm a little new to Ruby, so please feel free to suggest a completely
different and better way to do this, if you have one.  I'm trying to
figure out a way to access a variable within a singleton class
definition that is defined outside the singleton class definition.
Basically, I want to be able to add new, user-defined instance variables
and readers and writers for the instance variables to an object.  I can
do it fine if I construct the list of instance variables inline.  Given
a definition of MyClass, of course, the following code works
beautifully:

var = MyClass.new
class << var
  attr_accessor :field1, :field2, :field3
end

However, I need to be able to build the list prior to doing the
singleton class definition (ideally, I want to be able to pass the list
of instance variables into an instance method and have it take care of
the singleton class definition on itself).  This is the way code is
written right now:

class MyClass
  ...

  def add_fields(*field_list)
    class << self
      attr accessor *field_list
    end
  end
end

I've also tried the following in irb (identical to the above code that
works, except that the list of fields is assigned to a variable instead
of being constructed inline):

var = MyClass.new
list = :field1, :field2, :field3
class << var
  attr_accessor list
end

Both throw an error because field_list is not defined within the
singleton class definition?  Am I making a simple mistake, or should I
be doing this differently?

Thanks,
Doug G.
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