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APPENDIX A RUBY, A PROGRAMMER S BEST FRIEND
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teams = { :rowing => [[1982, "Hampton", "Catlin"], [1954, "Ryan", "McMinn"], ...], :track => [[1982, "Hampton", "Catlin"], [1900, "Mark", "Twain"], ...] }
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That works for now. But this is kind of ugly and we could very easily get confused, especially if we keep adding teams. This style of coding is referred to as procedural, and it s not object-oriented. We re just keeping track of huge data collections that are made up of simple types. Wouldn t it be nice to keep all of this data more organized
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Classes
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A class is like the blueprint for creating an object. We ve been using classes all over the place Array, String, User, and so on. They are the plans for how to build an object. Let s construct a Student class and a Team class. Here is the basic blueprint for a Student class:
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class Student def first_name=(value) @first_name = value end def first_name @first_name end def last_name=(value) @last_name = value end def last_name @last_name end def full_name @last_name + ", " + @first_name end end
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Right now, we re just keeping track of the student s first_name and last_name strings. As you can see, we defined a method named first_name=(value), and we take value and put it into an instance variable named @first_name. Let s try using this class we just made.
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# Take the Class, and turn it into a real Object instance @student = Student.new @student.first_name = "Lucas" @student.last_name = "Porter" puts @student.full_name
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"Porter, Lucas"
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So, instead of building a stupid array, we have built a smart class. We create an instance of the class called an object, by calling new on the class. It builds a version of itself called an object, which is then stored in the @student variable. In the next two lines, we use those = methods that we built to store the student s first and last name. Then we re able to use the method full_name to give a nicely formatted response. It turns out that creating reader and writer methods like we ve just done is a pretty common practice in object-oriented programming. Fortunately, Ruby saves us the effort of creating them by providing a shortcut: attr_accessor.
class Student attr_accessor :first_name, :last_name, :id_number def full_name @last_name + ", " + @first_name end end
This behaves in exactly the same way as the first version. The attr_accessor bit just helps us by automatically building the methods that we need, such as first_name=. Also, this time we added an @id_number. Let s build a Team class now.
class Team attr_accessor :name, :students def initialize(name) @name = name @students = [] end def add_student(id_number, first_name, last_name) student = Student.new student.id_number = id_number
APPENDIX A RUBY, A PROGRAMMER S BEST FRIEND
student.first_name = first_name student.last_name = last_name @students << student end def print_students @students.each do puts @student.full_name end end end
We have added something new to this class. We are using the initialize method. So, now when we call new, we can pass in the name. For example, we could say Team. new('baseball'), and the initialize method is then called. Not only is initialize setting up the name, it s also setting up an instance variable named @students and turning it into an empty array. The method add_students uses that array to fill it up with new Student objects. Let s see how we might use this class.
team = Team.new("Rowing") team.add_student(1982, "Hampton", "Catlin") team.add_student(1984, "Lucas", "Porter") team.print_students
Catlin, Hampton Lucas, Porter
Containing things in objects really cleans up our code. If we were going to build a
School class, it wouldn t be very complex. By using classes, we make sure that each object
needs to worry about only its own concerns. If we were writing this application without objects, everyone s business would be shared. The variables would all exist around each other, and there would basically be one huge object. Objects let us break things up into small working parts. By now, you should have a general idea of what is going on with some of the Ruby code that you have seen floating around Rails. There is a lot more to Ruby that we haven t even touched on here. Ruby has some really amazing metaprogramming features that you can read about in a book more specifically about Ruby, such as Beginning Ruby: From Novice to Professional by Peter Cooper (Apress, 2007).
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