custom_attributes.rb

module CustomAttributes
  def attributes(*attrs)
    attrs.each do |sym|
      define_method sym do
        instance_variable_get("@#{sym}")
      end
      define_method :"#{sym}=" do |v|
        instance_variable_set("@#{sym}", v)
      end
    end
  end
end

class Concrete
  extend CustomAttributes
  
  attributes :id
  
  def weird
    p id
    if false
      id = 69
    else
      p id
    end
  end
end

c = Concrete.new
c.id = 42
c.weird
# 42
# 69
# => 69