Class Methods & Inheritance

class_method.md

Class Methods

Quick Recap

Gems:

"can be used to extend or modify functionality in Ruby applications"

---

Ruby is an OOP (Almost everything is an object)

Instance Methods vs Class Methods

Source: Class vs Instance Methods

class SayHello
	# Class Method
  def self.from_the_class
    "Hello, from a class method"
  end
	# Instance Method
  def from_an_instance
    "Hello, from an instance method"
  end
end

Output:

>> SayHello.from_the_class
=> "Hello, from a class method"

>> SayHello.from_an_instance
=> undefined method `from_an_instance' for SayHello:Class


>> hello = SayHello.new
>> hello.from_the_class
=> undefined method `from_the_class' for #<SayHello:0x0000557920dac930>

>> hello.from_an_instance
=> "Hello, from an instance method"

Example

Finish 28_02_19_albums_class_challenge.rb

class_method_example.rb

# Create three classes: Artist, Album and Song
require 'pry'
require 'faker'

## Artist class
class Artist
	attr_accessor :albums
	attr_reader :num_artists
	@@num_artists = 0

	def initialize(name)
		@name = name
		@albums = []
		@@num_artists += 1
	end
	
	def add_album(album)
		@albums << album
	end   
	
	def album_count
		@albums.length
	end
	
	def self.count
		@@num_artists
	end
end

## Album class
class Album
	attr_accessor :songs
	attr_reader :num_albums
	@@num_albums = 0

	def initialize(title, release_date)
		@title = title
		@date = release_date
		@songs = []
		@@num_albums += 1
	end
	
	def add_song(song)
		@songs << song
	end
	
	def song_count
		@songs.length
	end

	def self.count
		@@num_albums
	end
end

## Song class
class Song
	def initialize(title, duration, genre)
		@title = title
		@duration = duration
		@genre = genre
	end
end

## Billboard class
class Billboard
	def artist_count
		return Artist.count
	end
end

## Making 30 random artists
artists = []
albums = []


30.times do 
	artist = Artist.new(Faker::Music.band)
	album = Album.new(Faker::Music.album, (2000..2010).to_a.sample)
	5.times { album.add_song(Song.new(Faker::Music::Phish.song, rand(5), Faker::Music.genre))}
	artist.add_album(album)
	
	artists << artist
	albums << album
end

billboard = Billboard.new
puts "Total number of Artists created: #{billboard.artist_count}"
puts "Total number of Albums created: #{Album.count}"

class_method_sample_solution.rb

# Create three classes: Artist, Album and Song
require 'pry'
require 'faker'

## Artist class
class Artist
	attr_accessor :albums
	attr_reader :num_artists
	@@num_artists = 0

	def initialize(name)
		@name = name
		@albums = []
		@@num_artists += 1
	end
	
	def add_album(album)
		@albums << album
	end   
	
	def album_count
		@albums.length
	end
	
	def self.count
		@@num_artists
	end
end

## Album class
class Album
	attr_accessor :songs
	attr_reader :num_albums
	@@num_albums = 0

	def initialize(title, release_date)
		@title = title
		@date = release_date
		@songs = []
		@@num_albums += 1
	end
	
	def add_song(song)
		@songs << song
	end
	
	def song_count
		@songs.length
	end

	def self.count
		@@num_albums
	end
end

## Song class
class Song
	def initialize(title, duration, genre)
		@title = title
		@duration = duration
		@genre = genre
	end
end

## Billboard class
class Billboard
	def artist_count
		return Artist.count
	end
end

## Making 30 random artists
artists = []
albums = []


30.times do 
	artist = Artist.new(Faker::Music.band)
	album = Album.new(Faker::Music.album, (2000..2010).to_a.sample)
	5.times { album.add_song(Song.new(Faker::Music::Phish.song, rand(5), Faker::Music.genre))}
	artist.add_album(album)
	
	artists << artist
	albums << album
end


billboard = Billboard.new
puts "Total number of Artists created: #{billboard.artist_count}"
puts "Total number of Albums created: #{Album.count}"

# binding.pry