Ruby Classes and Objects

In the above sample of code, the brand of soda always stays the same. But what if we want it to change? Well, we can use the class's constructor (the initialize method) to change it.

(Note: the constructor creates new objects as well as manipulates the data within them).

class Soda

def initialize(brand)

@brand = brand

end

def retrieve_brand

return @brand

end

end

soda = Soda.new("Pepsi")

puts "The soda brand is now " + soda.retrieve_brand

This will print the text: The soda brand is now Pepsi.

Attributes

In Ruby data items available outside of objects are known as Attributes. There are three types: Readable, Writeable, and Readable/Writeable.

To create a Readable attribute do the following:

class Soda

attr_reader :brand

def initialize(brand)

@brand = brand

end

end

soda = Soda.new("Dr. Salt")

puts "You are now drinking " + soda.brand

The result would be: You are now drinking Dr. Salt

The statement attr_read :brand creates an accessor method by the name (brand) and creates an instance variable of the same name (@brand). And that is how you create a readable attribute.

(Note: an accessor method allows you to access data inside an object).

To create a Writeable attribute do the following:

class Soda

attr_reader :brand

attr_writer :brand

def initialize(brand)

@brand = brand

end

end

soda = Soda.new("Pepsi")

puts "You are drinking " + soda.brand

soda.brand = "Dr. Salt"

puts "Sike...you are really drinking " + soda.brand

This outputs:

  You are drinking Pepsi

  Sike...you are really drinking Dr. Salt

Basically what happens is that you assign brand a value ("Pepsi"), read that brand and display it to the screen, then change the value using the writeable attribute to "Dr. Salt" and print that to the screen.

As you can see, we not only made a writeable attribute, but a readable one as well. There is a simpler method for creating a readable/writeable attribute however:

class Soda

attr_accessor :brand

def initialize(brand)

@brand=brand

end

end

soda = Soda.new("Pepsi")

puts soda.brand + " Cola burnt him up"

soda.brand = "7-UP."

puts "Now he's drinking " + soda.brand

This would create the following result:

  Pepsi Cola burnt him up

  Now he's drinking 7-UP.