[Ruby] LEVEL 2 Methods and Classes -- Ex

Optional Arguments

We'll store a little more information about our games than just the name. Optional arguments are important for a flexible interface. Let's change our new_game method so it can be called without passing in year or system.

def new_game(name, year, system)
  {
    name: name,
    year: year,
    system: system
  }
end
game = new_game("Street Figher II", nil, nil)

Answer:

def new_game(name, year=nil, system=nil)
  {
    name: name,
    year: year,
    system: system
  }
end
game = new_game("Street Figher II")

 

Options Hash Argument

Defaulting two arguments to nil isn't ideal. Update the method signature and implementation to take an optional optionshash with keys for :year and :system.

def new_game(name, year=nil, system=nil)
  {
    name: name,
    year: year,
    system: system
  }
end
game = new_game("Street Figher II", "SNES", 1992)

Answer:

def new_game(name, options={})
  {
    name: name,
    year: options[:year],
    system: options[:system]
  }
end
game = new_game("Street Figher II",
  year: 1992,
  system: "SNES")

 

Raise Exception

We want to make sure that each game is a valid game object - in this case a simple hash of values. Even still, we wouldn't want to return a hash with a nil name. Raise an InvalidGameError error in the new_game method if name is nil.

class InvalidGameError < StandardError; end
def new_game(name, options={})
  {
    name: name,
    year: options[:year],
    system: options[:system]
  }
end
begin
  game = new_game(nil)
rescue InvalidGameError => e
  puts "There was a problem creating your new game: #{e.message}"
end

Answer:

class InvalidGameError < StandardError; end
def new_game(name, options={})
  raise InvalidGameError, "You must provide a name for the game" unless name
  {
    name: name,
    year: options[:year],
    system: options[:system]
  }
end
begin
  game = new_game(nil)
rescue InvalidGameError => e
  puts "There was a problem creating your new game: #{e.message}"
end

 

Splat Arguments

When passing in an array of arguments to a method, sometimes it'll make sense to use Ruby's "splat" operator rather than explicitly requesting an array. Update the describe_favorites method and the call to it to instead use the splat operator.

def describe_favorites(*games)
  for game in games
    puts "Favorite Game: #{game}"
  end  
end
describe_favorites(['Mario', 'Contra', 'Metroid'])

Answer:

def describe_favorites(*games)
  for game in games
    puts "Favorite Game: #{game}"
  end  
end
describe_favorites('Mario', 'Contra', 'Metroid')

 

Class

Passing around hashes is getting troublesome, let's use a class to hold our data. We've started the Game class for you, now please implement the initialize method to store name, system and year in instance variables.

class Game
  def initialize(name, options={})
  end
end

Answer:

class Game
  def initialize(name, options={})
    @name = name
    @year = options[:year]
    @system = options[:system]
  end
end

 

attr_accessor

Whoever created the game object will want to be able to access the name, year and system for the game, but that doesn't mean we need to make getter methods for them. Refactor the code below to make these variables available using the Ruby way with attr_accessor.

class Game
  def initialize(name, options={})
    @name = name
    @year = options[:year]
    @system = options[:system]
  end

  def name
    @name
  end

  def year
    @year
  end

  def system
    @system
  end
end

Answer:

class Game
  attr_accessor :year, :system, :name
  
  def initialize(name, options={})
    @name = name
    @year = options[:year]
    @system = options[:system]
  end
end

 

attr_reader

When a game is initialized, store another variable called created_at which is set to Time.now in the initialize method. Make sure it can be accessed, but that it cannot be set from outside the object.

class Game
  attr_accessor :name, :year, :system

  def initialize(name, options={})
    @name = name
    @year = options[:year]
    @system = options[:system]
  end
end

Answer:

class Game
  attr_accessor :name, :year, :system
  attr_reader :created_at

  def initialize(name, options={})
    @name = name
    @year = options[:year]
    @system = options[:system]
    @created_at = Time.now
  end
end