From PHP to Ruby on Rails by Bernard Pineda

Author:Bernard Pineda
Language: eng
Format: epub
Publisher: Packt Publishing Pvt Ltd
Published: 2023-11-16T00:00:00+00:00

Inheritance in Ruby

So far, we’ve looked at a few features that come with Ruby’s implementation of the OOP paradigm, but we have neglected to look at one of the core features that help us recycle code. Inheritance can be simplified as the practice of passing the features of a class to create a brand-new child class. With this new class, we can use any of the features from the parent class, create new features, or customize the features that come from the parent class. The syntax for inheritance can be quite different than in PHP, but the behavior is quite similar. With that in mind, let’s take a look at a few use cases and see it in action.

Let’s say we wanted a class that would let us connect to a database. Instead of having to write all the functionality to connect to a database, we could get an already created database class, create a new one that inherited all the database functionality, and then focus on creating just the features that we need. This is one way to reuse code with inheritance, but let’s use a simpler example so that we can see inheritance in practice. Let’s say we wanted to make an abstraction of a user. The user must have first name, last name, age, and email details. We can take the Person class, defined in the previous section, inherit the features in our new User class, and just focus on the missing pieces.

So, let’s take our Person class and create a file called inheritance_example.rb with the following content:

# inheritance_example.rb class Person attr_accessor :first_name, :last_name def initialize( first_name, last_name ) @first_name = first_name @last_name = last_name end def full_name puts "#{first_name} #{last_name}" end end

Now, let’s create a new class below our original class called User and inherit from the Person class. We’ll do this with the < operator. Let’s add this to the end of our Person class:

# inheritance_example.rb … class User < Person end

With just two lines of code, we’ve made a brand-new class that behaves (for now) in the exact same way as the Person class. Let’s confirm that by creating a new User object. Let’s now add the following to the end of our file:

# inheritance_example.rb … user = User.new

Now, let’s try to run this script from our shell:

ruby inheritance_example.rb

This should output the following:

inheritance_example.rb:4:in `initialize': wrong number of arguments (given 0, expected 2) (ArgumentError) from inheritance_example.rb:18:in `new' from inheritance_example.rb:18:in `<main>'

Our script failed, but why? As we read through the message, it states that the constructor expected two parameters, but none were given. From our previous execution example, we can infer that we have to give our constructor the parameters for the first name and last name. So, let’s add those parameters, and let’s also call the full_name() method. Our code will now look like this:

class Person attr_accessor :first_name, :last_name def initialize( first_name, last_name ) @first_name = first_name @last_name = last_name end def full_name puts "#{first_name} #{last_name}" end end class User < Person end user = User.

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