Ruby Class Methods

Prerequisites

• ruby-objects-self

Objectives

By the end of this, developers should be able to:

• Give an example of a class method you already use.
• Diagram the invocation pattern between #initialize and .new.
• Contrast defining class methods with defining instance methods.
• Contrast invoking class methods with invoking instance methods.

Preparation

1. Fork and clone this repository. FAQ
2. Create a new branch, training, for your work.
3. Checkout to the training branch.
4. Install dependencies with bundle install.

Demo: Class Methods

Sometimes a method is associated with a class, not an object.

Observe how a Method on a Class differs from a method on an Instance that Class.

Let's discuss the code below in lib/pet.rb

In the Animal class, and the ::new method is recieved by the Animal class, with 'Zeno' and 'cat' as an arguments. It then calls the instance method #initialize with 'Zeno' and 'cat' as an arguments, which assigns 'Zeno' to an instance variable, @name and 'cat' to the instance variable @species.

The Pet class is different. The Pet class is used here to give us meta-data about a list of Pets. When we get to Rails, this data will be information we get back from the database.

Where will the method dog_count be recieved? What about all?

Lab: Make a Class Method

• Make a class method, search on Album (in lib/album.rb) to search the collection of songs by title.
• Make a class method count that returns the total number of songs on the album.
• Use bin/rake test to test your work

Bonus:

• Make your search be insensitive to case ('Formation' and 'formation' return the same song)
• Make the search look for part of a word ('ation' also returns the song 'Formation')

License

1. All content is licensed under a CC­BY­NC­SA 4.0 license.
2. All software code is licensed under GNU GPLv3. For commercial use or alternative licensing, please contact legal@ga.co.