gistfile1.rb

class Test
  def initialize
    @atts = Hash.new
  end

  def prop=(value)
    @atts[:prop] = value
  end

  def prop
    @atts[:prop]
  end

  def set_prop(value)
    prop = value
  end
end

t = Test.new
t.set_prop 'a'
puts t.prop.nil?