Learn Ruby The Hard Way #43

Question

Can someone please explain me what is happening here? I know that this code is simple, but it is hard for me, I am ultimate beginner. I am stucked for many hours here, I cant figure it out.. When I run code, CentralCorridor class is run where we have basic gets.chomp prompt. All answers("shoot!", "dodge!", "tell a joke") for that prompt end program. I dont know how to enter to other scenes (class TheBridge, class EscapePod, class LaserWeaponArmory...). I really want to make my own game like this, but i cant figure it out.. Also, if someone can explain me this enter() method. Please help :) here is link: http://ruby.learncodethehardway.org/book/ex43.html or code:

class Scene 
  def enter() # what this method do?
    exit(1)
  end
end

class Engine 

  def initialize(scene_map)
    @scene_map = scene_map
  end

  def play()
    current_scene = @scene_map.opening_scene()
    last_scene = @scene_map.next_scene('finished')

    while current_scene != last_scene
      next_scene_name = current_scene.enter()
      current_scene = @scene_map.next_scene(next_scene_name)
    end

    # be sure to print the last scene
    current_scene.enter()
  end
end

class Death < Scene

  @@quips = [
    "You died. You kinda suck at this",
     "Your mom would be proud...if she were smarter.",
     "Such a luser.",
     "I have a small puppy that's better at this."
  ]

  def enter()
    puts @@quips[rand(0..(@@quips.length - 1))] # 2. what is this?
    exit(1)
  end
end

class CentralCorridor < Scene

  def enter()
    puts "The Gothons of Planet Percal #25 have invaded your ship and destroyed"
    puts "your entire crew.  You are the last surviving member and your last"
    puts "mission is to get the neutron destruct bomb from the Weapons Armory,"
    puts "put it in the bridge, and blow the ship up after getting into an "
    puts "escape pod."
    puts "\n"
    puts "You're running down the central corridor to the Weapons Armory when"
    puts "a Gothon jumps out, red scaly skin, dark grimy teeth, and evil clown costume"
    puts "flowing around his hate filled body.  He's blocking the door to the"
    puts "Armory and about to pull a weapon to blast you."
    print "> "

    action = $stdin.gets.chomp

    if action == "shoot!"
      puts "Quick on the draw you yank out your blaster and fire it at the Gothon."
      puts "His clown costume is flowing and moving around his body, which throws"
      puts "off your aim.  Your laser hits his costume but misses him entirely.  This"
      puts "completely ruins his brand new costume his mother bought him, which"
      puts "makes him fly into an insane rage and blast you repeatedly in the face until"
      puts "you are dead.  Then he eats you."
      return 'death'

    elsif action == "dodge!"
      puts "Like a world class boxer you dodge, weave, slip and slide right"
      puts "as the Gothon's blaster cranks a laser past your head."
      puts "In the middle of your artful dodge your foot slips and you"
      puts "bang your head on the metal wall and pass out."
      puts "You wake up shortly after only to die as the Gothon stomps on"
      puts "your head and eats you."
      return 'death'

    elsif action == "tell a joke"
      puts "Lucky for you they made you learn Gothon insults in the academy."
      puts "You tell the one Gothon joke you know:"
      puts "Lbhe zbgure vf fb sng, jura fur fvgf nebhaq gur ubhfr, fur fvgf nebhaq gur ubhfr."
      puts "The Gothon stops, tries not to laugh, then busts out laughing and can't move."
      puts "While he's laughing you run up and shoot him square in the head"
      puts "putting him down, then jump through the Weapon Armory door."
      return 'finished'

    else
      puts "DOES NOT COMPUTE!"
      return 'central_corridor'
    end
  end
end

class LaserWeaponArmory < Scene

  def enter()
    puts "You do a dive roll into the Weapon Armory, crouch and scan the room"
    puts "for more Gothons that might be hiding.  It's dead quiet, too quiet."
    puts "You stand up and run to the far side of the room and find the"
    puts "neutron bomb in its container.  There's a keypad lock on the box"
    puts "and you need the code to get the bomb out.  If you get the code"
    puts "wrong 10 times then the lock closes forever and you can't"
    puts "get the bomb.  The code is 3 digits."
    code = "#{rand(1..9)}#{rand(1..9)}#{rand(1..9)}"
    print "[keypad]> "
    guess = $stdin.gets.chomp
    guesses = 0

    while guess != code && guesses < 10
      puts "BZZZZEDDD!"
      guesses += 1
      print "[keypad]> "
      guess = $stdin.gets.chomp
    end

    if guess == code
        puts "The container clicks open and the seal breaks, letting gas out."
        puts "You grab the neutron bomb and run as fast as you can to the"
        puts "bridge where you must place it in the right spot."
        return 'the_bridge'
    else
        puts "The lock buzzes one last time and then you hear a sickening"
        puts "melting sound as the mechanism is fused together."
        puts "You decide to sit there, and finally the Gothons blow up the"
        puts "ship from their ship and you die."
        return 'death'
    end
  end
end


class TheBridge < Scene

  def enter()
    puts "You burst onto the Bridge with the netron destruct bomb"
    puts "under your arm and surprise 5 Gothons who are trying to"
    puts "take control of the ship.  Each of them has an even uglier"
    puts "clown costume than the last.  They haven't pulled their"
    puts "weapons out yet, as they see the active bomb under your"
    puts "arm and don't want to set it off."
    print "> "

    action = $stdin.gets.chomp

    if action == "throw the bomb"
      puts "In a panic you throw the bomb at the group of Gothons"
      puts "and make a leap for the door.  Right as you drop it a"
      puts "Gothon shoots you right in the back killing you."
      puts "As you die you see another Gothon frantically try to disarm"
      puts "the bomb. You die knowing they will probably blow up when"
      puts "it goes off."
      return 'death'

    elsif action == "slowly place the bomb"
      puts "You point your blaster at the bomb under your arm"
      puts "and the Gothons put their hands up and start to sweat."
      puts "You inch backward to the door, open it, and then carefully"
      puts "place the bomb on the floor, pointing your blaster at it."
      puts "You then jump back through the door, punch the close button"
      puts "and blast the lock so the Gothons can't get out."
      puts "Now that the bomb is placed you run to the escape pod to"
      puts "get off this tin can."
      return 'escape_pod'
    else
      puts "DOES NOT COMPUTE!"
      return "the_bridge"
    end
  end
end


class EscapePod < Scene

  def enter()
    puts "You rush through the ship desperately trying to make it to"
    puts "the escape pod before the whole ship explodes.  It seems like"
    puts "hardly any Gothons are on the ship, so your run is clear of"
    puts "interference.  You get to the chamber with the escape pods, and"
    puts "now need to pick one to take.  Some of them could be damaged"
    puts "but you don't have time to look.  There's 5 pods, which one"
    puts "do you take?"

    good_pod = rand(1..5)
    print "[pod #]> "
    guess = $stdin.gets.chomp.to_i

    if guess != good_pod
      puts "You jump into pod %s and hit the eject button." % guess
      puts "The pod escapes out into the void of space, then"
      puts "implodes as the hull ruptures, crushing your body"
      puts "into jam jelly."
      return 'death'
    else
      puts "You jump into pod %s and hit the eject button." % guess
      puts "The pod easily slides out into space heading to"
      puts "the planet below.  As it flies to the planet, you look"
      puts "back and see your ship implode then explode like a"
      puts "bright star, taking out the Gothon ship at the same"
      puts "time.  You won!"


      return 'finished'
    end
  end
end

class Finished < Scene
  def enter()
    puts "You won! Good job."
  end
end

class Map
  @@scenes = {
    'central_corridor' => CentralCorridor.new(),
    'laser_weapon_armory' => LaserWeaponArmory.new(),
    'the_bridge' => TheBridge.new(),
    'escape_pod' => EscapePod.new(),
    'death' => Death.new(),
    'finished' => Finished.new(),
  }


  def initialize(start_scene)
    @start_scene = start_scene
  end


  def next_scene(scene_name)
    val = @@scenes[scene_name]
    return val
  end

  def opening_scene()
    return next_scene(@start_scene)
  end
end

a_map = Map.new('central_corridor')
a_game = Engine.new(a_map)
a_laser = EscapePod.new()
a_game.play()

Answer 1

Aleksar

You have a game with a number of components:

The Engine - the main entry point to the game (you can tell because it has the play method) You've got a Map object which is just a collection of the different scenes that can be played in the game. Each scene is just another scenario in the game with its own challenges. E.g. in on scene you are on the bridge in another you are in an escape pod. In another you have a weapon whatever.

All of scenes in the game inherit their behavior from the Scene class as in this example.

class EscapePod < Scene
#....
#Scene stuff
#...
end

The code above basically says create a class called EscapePod that can do everything that a Scene can do.

What is throwing you off is that the Scene class doesn't do much. It has only one behavior (this is a slight over simplification) which is it that it knows how to do something called enter which in this case just immediately exits. This Scene class is a template for all of the other scenes that are more interesting.

class Scene 
 def enter() # what this method do?
  exit(1)
 end
end

Each scene subclass overrides the enter method from the template to do something more interesting when enter is called rather than just exiting.

The next simplest scene is the Finish scene it is a little more interesting it tells you did a good job.

class Finished < Scene
  def enter()
  puts "You won! Good job."
 end
end

One last thing. It is clear that intention is not to use Scene class directly but only the subclasses EscapePod, Finish etc. which must override the enter method.

If this were production code you might even see something like this:

class Scene 
 def enter() # what this method do?
  raise "Scene 'enter' must not be used directly.Please subclass Scene and provide a meaningful    implementation for the 'enter' method" 
 end
end

I hope this helps.