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 Ruby: Class

Class definition:

class Song
  def initialize(name, artist, duration)
    @name     = name
    @artist   = artist
    @duration = duration
  end
end

The initialize method is called after a new instance of a class is created:

aSong = Song.new("Bicylops", "Fleck", 260) 

You can add to a class subsequent to it's definition:

class Song  
  def to_s  
    "Song: #{@name}--#{@artist} (#{@duration})"  
  end  
end  
aSong = Song.new("Bicylops", "Fleck", 260)  
aSong.to_s  » "Song: Bicylops--Fleck (260)"  

A class can be created based on another class using inheritance:

class KaraokeSong < Song
  def initialize(name, artist, duration, lyrics)
    super(name, artist, duration)
    @lyrics = lyrics
  end
end

Ruby only supports single-inheritance.

In the above example, KaraokeSong is a subclass of Song, and Song is the superclass of KaraokeSong.

In the above example, super causes the same method of the object's parent object to be called. In this case, the parents initialize method is called.

A class instance's instance variables are private, they can not be accessed by code external to the class. Ruby provides a shortcut to create accessor methods:

class Song  
  attr_reader :name, :artist, :duration  
end  

This generates code equivalent to:

class Song  
  def name  
    @name  
  end  
  def artist  
    @artist  
  end  
  def duration  
    @duration  
  end  
end  

Ruby provides a shortcut to create attribute setters:

class Song
  attr_writer :duration
end

This generates code equivalent to:

class Song  
  def duration=(newDuration)  
    @duration = newDuration  
  end  
end  

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