try_and_try_again

gist-1.rb

class Project
  attr_reader :supervisor

  # assume supervisor looks like:
  # ["Harry", "Henderson", "[email protected]"]

  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", "[email protected]")

  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", "[email protected]")

  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

gist-5.rb

require 'rubygems'
require 'rumonade'
include Rumonade

class Project
  attr_reader :supervisor # this is now an Option of Supervisor (this is a "monad")

  # assume supervisor looks like:
  # Supervisor.new("Harry", "Henderson", "[email protected]")

  def initialize(supervisor=None)
    @supervisor = supervisor
  end
end

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

## Exposing the option to user of class
puts Project.new.supervisor
# => None 
puts Project.new(Supervisor.new("Arthur", "Dent")).map(&:display_name).get_or_else("No supervisor assigned.")
# => Arthur, Dent
puts Project.new.supervisor.map(&:display_name).get_or_else("No supervisor assigned.")
# => No supervisor assigned.

gist-6.rb

require 'rubygems'
require 'rumonade'
include Rumonade

class Project
  attr_reader :supervisor
  
  # assume supervisor looks like:
  # Supervisor.new("Harry", "Henderson", "[email protected]")

  def initialize(supervisor=nil)
    @supervisor = supervisor
  end
  
  def supervisor_display_name
    Option(supervisor).map(&:display_name).get_or_else("No supervisor assigned.")
  end  
end

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

## Option used internally, not exposed to user of class
puts Project.new.supervisor
# => 
puts Project.new(Supervisor.new("Arthur", "Dent")).supervisor_display_name
# => Arthur, Dent
puts Project.new.supervisor_display_name
# => No supervisor assigned.