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Structs: Quick and Easy Data Classes
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One thing should stand out about the main code listing so far. It s repetitive. The Room and Player classes are merely acting as basic placeholders for data rather than as true classes with logic and functionality. There s an easier way to create this sort of special data-holding class in Ruby with a single line of a class called a Struct. A struct is a special class whose only job is to have attributes and to hold data. Here s a demonstration:
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Person = Struct.new(:name, :gender, :age) fred = Person.new("Fred", "male", 50) chris = Person.new("Chris", "male", 25) puts fred.age + chris.age
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Simply, the Struct class builds classes to store data. On the first line you create a new class called Person that has built-in name, gender, and age attributes. On the second line you create a new object instance of Person and set the attributes on the fly. The first line is equivalent to this longhand method:
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class Person attr_accessible :name, :gender, :age
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CHAPTER 6 CLASSES, OBJECTS, AND MODULES
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def initialize(name, gender, age) @name = name @gender = gender @age = age end end
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Note In actuality, this code is not exactly equivalent to the struct code, because parameters are optional
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when initializing a Struct class, whereas the preceding Person class code requires the three parameters (name, gender, and age) be present.
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This code creates a Person class the long way. If all you want to do is store some data, then the struct technique is quicker to type and easier to read, although if you ultimately want to add more functionality to the class, creating a class the long way is worth the effort. However, the good thing is that you can start out with a struct and recode it into a full class when you re ready. This is what you re going to do with your dungeon. Let s rewrite it from scratch:
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class Dungeon attr_accessor :player def initialize(player_name) @player = Player.new(player_name) @rooms = [] end Player = Struct.new(:name, :location) Room = Struct.new(:reference, :name, :description, :connections) end
It s certainly shorter, and because parameters are optional when creating instances of Struct classes, you can still use Player.new(player_name), and the location attribute is merely set to nil. If you ever need to add methods to Player or Room, you can rewrite them as classes and add the attributes back with attr_accessor.
CHAPTER 6 CLASSES, OBJECTS, AND MODULES
ATTR_ACCESSOR
Throughout the code in this chapter, as well as that in 2, you have used attr_accessor within classes to provide attributes for your objects. attr_accessor allows you to do this:
class Person attr_accessor :name, :age end x = Person.new x.name = "Fred" x.age = 10 puts x.name, x.age
However, in reality, attr_accessor isn t doing anything magical. It s simply writing some code for you. This code is equivalent to the single attr_accessor :name, :age line in the preceding Person class:
class Person def name @name end def name=(name) @name = name end def age @age end def age=(age) @age = age end end
This code defines the name and age methods that return the current object variables for those attributes, so that x.name and x.age (as in the prior code) work. It also defines two setter methods that assign the values to the @name and @age object variables. If you pay attention to the names of the setter methods, you ll see they re the same as the methods that return values but suffixed with an equal sign (=). This means they re the methods that are run for code such as x.name = "Fred" and x.age = 10. In Ruby, assignments are just calls to regular methods! Indeed, x.name = "Fred" is merely shorthand for writing x.name=("Fred").
CHAPTER 6 CLASSES, OBJECTS, AND MODULES
Creating Rooms
Your dungeon now has the basic classes in place, but there s still no way to create rooms, so let s add a method to the Dungeon class:
class Dungeon def add_room(reference, name, description, connections) @rooms << Room.new(reference, name, description, connections) end end
You want to add rooms to the dungeon, so adding a method to dungeon objects makes the most sense. Now you can create rooms like so (if my_dungeon is still defined, of course):
my_dungeon.add_room(:largecave, "Large Cave", "a large cavernous cave", { :west => :smallcave }) my_dungeon.add_room(:smallcave, "Small Cave", "a small, claustrophobic cave", { :east => :largecave }) add_room accepts the reference, name, description, and connections arguments and creates a new Room object with them before pushing that object onto the end of the @rooms array. The reference, name, and descriptions arguments should seem obvious, but the connections argument is designed to accept a hash that represents the connections that a particular room has with other rooms. For example, { :west => :smallcave } ties two symbols (:west and :smallcave) together. Your dungeon logic uses this link to connect the rooms. A connections hash of { :west => :smallcave, :south => :another_room } creates two connections (one to the west, and one to the south).
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