class Name
  # Define default getter methods, but not setter methods.
  attr_reader :first, :last
  # When someone tries to set a first name, enforce rules about it.
  def first=(first)
    if first == nil or first.size == 0
      raise ArgumentError.new('Everyone must have a first name.')
    end
    first = first.dup
    first[0] = first[0].chr.capitalize
    @first = first
  end
  # When someone tries to set a last name, enforce rules about it.
  def last=(last)
    if last == nil or last.size == 0
      raise ArgumentError.new('Everyone must have a last name.')
    end
    @last = last
  end
  def full_name
    "#{@first} #{@last}"
  end
  # Delegate to the setter methods instead of setting the instance
  # variables directly.
  def initialize(first, last)
    self.first = first
    self.last = last
  end
end
jacob = Name.new('Jacob', 'Berendes')
jacob.first = 'Mary Sue'
jacob.full_name

john = Name.new('john', 'von Neumann')
john.full_name

john.first = 'john'
john.first

john.first = nil

ArgumentError: Everyone must have a first name.
...

ArgumentError: Everyone must have a first name.
	from (irb):7:in `first='
	from (irb):37

Name.new('Kero, international football star and performance artist', nil)

ArgumentError: Everyone must have a last name.
...

ArgumentError: Everyone must have a last name.
	from (irb):16:in `last='
	from (irb):27:in `initialize'
	from (irb):38

class SimpleContainer
  attr_accessor :value
end
c = SimpleContainer.new
c.respond_to? "value="

c.value = 10; c.value

c.value = "some random value"; c.value

c.value = [nil, nil, nil]; c.value