Self, Getter and Setter methods and initialize, accessors concepts explained in Ruby

While I was reviewing some concepts in Ruby, I thought it would be nice to make an article about some of main concepts. I will be touching basic concepts of Ruby. However, they are crucial topics.

Self

Self is a keyword in Ruby representing the default object of the current context.

So, in picture 1, we have a class method Drink, this Drink class have a method called show_yourself in line 15. and in picture 2, we have 2 instance of this Drink class. one martini, the other mach.

picture 1

picture 2

So, let’s look out our pry to see what show_yourself method gives us. When you look at picture 3, martini.show_yourself gives us <Drink:0x0007…>

The self keyword refers to the instance, or object, that the #show_yourself method is being called on. So, when we call #show_yourself on martini, the method will puts out to the terminal the Drink instance that is martini.

picture 3

I guess we are done with this example. How about when we make a method like in picture 4.

picture 4

When we type a method with in front of self keyword, we made a class method.

If we type this method on binding.pry. It will gives us Drink class itself.

Getter Method

# this part I took everything from dev.to. They explain concept very well.

A getter method is a method that gets a value of an instance variable.
Without a getter method, you can not retrieve a value of an instance variable outside the class the instance variable is instantiated from.

class Movie
  def initialize(name)
    @name = name
  end
end

obj1 = Movie.new('Forrest Gump')
p obj1.name #=> undefined method `name' for #<Movie:0x007fecd08cb288 @name="Forrest Gump"> (NoMethodError)

As you can see, the value of obj1 (name) can not be retrieved outside Movie class. if you try to retrieve a value of an instance variable outside its class without a getter method, Ruby raises No Method Error.

Now, Let’s see how to retrieve the value of obj1 outside Movie class with a getter method.
All you have to do here is to define a getter method named name. Though the name of a getter method can be anything, it is common practice to name a getter method the instance variable’s name.

class Movie
  def initialize(name)
    @name = name
  end

  def name
    @name
  end
end

obj1 = Movie.new('Forrest Gump')
p obj1.name #=> "Forrest Gump"

Setter Method

# this part I took everything from dev.to. They explain concept very well.

A setter is a method that sets a value of an instance variable.
Without a setter method, you can not assign a value to an instance variable outside its class.
if you try to set a value of an instance variable outside its class, Ruby raises No Method Error just like it does when you try to retrieve a value of an instance variable outside its class without a getter method.

class Movie
  def initialize(name)
    @name = name
  end

  def name #getter method
    @name
  end
end

obj1 = Movie.new('Forrest Gump')
p obj1.name #=> "Forrest Gump"
obj1.name = 'Fight Club' #=> undefined method `name=' for #<Movie:0x007f9937053368 @name="Forrest Gump"> (NoMethodError)

Defining a setter method inside a class makes it possible to set a value of an instance variable outside the class.
You can define a setter method like the code below.

class Movie
  def initialize(name)
    @name = name
  end

  def name #getter method
    @name
  end

  def name=(name) #setter method
    @name = name
  end
end

obj1 = Movie.new('Forrest Gump')
p obj1.name #=> "Forrest Gump"
obj1.name = 'Fight Club'
p obj1.name #=> "Fight Club"

By using name=, you can now assign a new value Fight Club to obj1.

Accessors

# this part I took everything from dev.to. They explain concept very well.

Accessors are a way to create getter and setter methods without explicitly defining them in a class.
There are three types to accessors in Ruby.

• attr_reader automatically generates a getter method for each given attribute.
• attr_writer automatically generates a setter method for each given attribute.
• attr_accessor automatically generates a getter and setter method for each given attribute.

First, let’s take a look at attr_reader!
As you can see in the code below, name and year are retrieved outside Movie class even though there is no getter method for either of them. This is because attr_reader generates a getter method for each given attribute.

class Movie
  attr_reader :name, :year

  def initialize(name, year)
    @name = name
    @year = year
  end
end
obj1 = Movie.new('Forrest Gump', 1994)
p obj1.name #=> Forrest Gump
p obj1.year #=> 1994

Second, let’s see how attr_writer works!
As I mentioned above, attr_witer generates a setter method for each given attribute. Therefore you can assign new values to ob1 without explicitly writing setter methods for name and year!

class Movie
  attr_reader :name, :year 
  attr_writer :name, :year

  def initialize(name, year)
    @name = name
    @year = year
  end
end
obj1 = Movie.new('Forrest Gump', 1994)
obj1.name = 'Fight Club'
obj1.year = 1999
p obj1.name #=> "Fight Club"
p obj1.year #=> 1999

Last but certainly not least, attr_accessor does what attr_reader and attr_writer do with just one line of code! It will automatically generate a getter and setter mehod for each given attribute.

class Movie
  attr_accessor :name, :year

  def initialize(name, year)
    @name = name
    @year = year
  end
end
obj1 = Movie.new('Forrest Gump', 1994)
obj1.name = 'Fight Club'
obj1.year = 1999
p obj1.name #=> "Fight Club"
p obj1.year #=> 1999

Initialize

# this part I took everything from learn co. They explain concept very well.

class Dog
end

snoopy = Dog.new #=> #<Dog:0x007f970a2edfd0>

The code above creates a new instance of the Dog class and sets that object equal to a variable, snoopy. If we want to give our dog a breed, we have to use the following code:

class Dog
  def breed=(breed)
    @breed = breed
  end

  def breed
    @breed
  end
end

snoopy = Dog.new #=> #<Dog:0x007f970a2edfd0>
snoopy.breed #=> nil
snoopy.breed = "Beagle"
snoopy.breed #=> "Beagle"

However, most dogs are born with a breed, not assigned a breed afterwards. How can we model the behavior of dogs being born with a breed in our Dog class? If only there was a way for us to assign an individual dog a breed automatically upon creation, or instantiation.

Lucky for us, there is! It’s called the #initialize method.

The #initialize Method

We already know that any Ruby class can produce new instances of itself, via the <Class Name>.new method, whether or not that class has an #initialize method. However, if we want each instance of our class to be created with certain attributes, we must define an #initialize method. An #initialize method is a method that is called automatically whenever #new is used.

Let’s define an #initialize method that takes in an argument of a dog's breed and sets a @breed variable equal to that argument. In other words, let's define our #initialize method to contain the functionality of the #breed= method, so that a dog instance will get a breed assigned to it right away when it is created, without us having to explicitly use the #breed= method.

class Dog
  def initialize(breed)
    @breed = breed
  end
  def breed=(breed)
    @breed = breed
  end
  def breed
    @breed
  end
end

Now, we can call #new like this:

lassie = Dog.new("Collie")
lassie.breed #=> "Collie"

References

Ruby Self - Learn.co

Ruby Getters and Setters

Ruby Initialization - Learn.co