try_and_try_again

gist-1.rb

class Project
  attr_reader :supervisor

  # assume supervisor looks like:
  # ["Harry", "Henderson", "hhendersonfake@me.com"]

  def initialize(supervisor)
    @supervisor = supervisor
  end

  def display_name
    if supervisor
      supervisor[0] + ", " + supervisor[1] # yuck
    else
      "No supervisor assigned."
    end
  end
end

gist-2.rb

class Project
  attr_reader :supervisor

  # assume supervisor looks like:
  # Supervisor.new("Harry", "Henderson", "hhendersonfake@me.com")

  def initialize(supervisor)
    @supervisor = supervisor
  end
end

Supervisor = Struct.new(:first_name, :last_name, :email) do
    def display_name
      if !first_name.nil? || !last_name.nil?
        first_name + ", " + last_name
      else
        "No supervisor assigned."
      end
    end
  end

gist-3.rb

NullSupervisor = Struct.new() do
  def display_name
    "No supervisor assigned."
  end
end

gist-4.rb

class Project
  attr_reader :supervisor

  # assume supervisor looks like:
  # Supervisor.new("Harry", "Henderson", "hhendersonfake@me.com")

  def initialize(supervisor=NullSupervisor.new)
    @supervisor = supervisor
  end
end

Supervisor = Struct.new(:first_name, :last_name, :email) do
  def display_name
    first_name + ", " + last_name
  end
end

NullSupervisor = Struct.new() do
  def display_name
    "No supervisor assigned."
  end
end