testing ruby object for attribute presence/absence

widget.rb

class Widget
  attr_accessor :circumference
  attr_accessor :colour
  attr_accessor :mass
  
  def initialize(attributes)
    attributes.each do |key, value|
      m = "#{key}=".to_sym
      self.send(m, value) if self.respond_to?(m)
    end
  end
end

widget = Widget.new({circumference:1})

# test for presence of attributes
puts widget.circumference.nil?
puts widget.colour.nil?

% ruby widget.rb
false
true