AssanSav / ruby-super-inheritance-

Ruby Inheritance: Using the super Keyword

Introduction

So far, we've seen the benefits of using inheritance to create a group of classes that share certain characteristics and behaviors. However, up until now, the implementation of shared characteristics has been somewhat rigid. If class Student inherits from class User, we can choose to either allow the Student class to inherit a certain method from User or overwrite that method with another implementation that is specific to Student.

But what if there is a method in the parent class that we want our child to share some of the functionality of? Or what if we want our child class to inherit a method from the parent and then augment it in some way? We can achieve this with the use of the super keyword.

Using super to supercharge inheritance

Let's say we are working on an education app in which users are either students or teachers. We have a parent, User class, that both our Student and Teacher classes inherit from.

Our User class has a method, log_in, that sets an instance variable, @logged_in equal to true.

class User

  def log_in
    @logged_in = true
  end
end

However, when a student logs into our app, we need to not only set their logged in attribute to true, we need to set their "in class" attribute to true. We could simply edit the #log_in method in the User class to account for this. But that doesn't make sense here. Remember that both Student and Teacher inherit from User. Teachers don't need to indicate that they are "in class", so we don't want to alter the #log_in method of our parent class and inadvertently give teachers some behavior that they don't want or need.

Instead, we can augment, or supercharge, the #log_in method inside of the Student class.

Let's take a look:

class Student < User
  def log_in
    super
    @in_class = true
  end
end

Here, we re-define the #log_in method and tell it to inherit any functionality of the #log_in method defined in the parent, or "super", class, which is User.

In the #log_in method above, the super keyword will call on the #log_in method as defined in the super class. Then, the additional code that we're adding into our Student#log_in method will also run. We have therefore supercharged our #log_in method, for the Student class only.

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