Tenzin Chemi

Ruby: What is a class variable?

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Tenzin Chemi
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Class variable

Class variables are variables prefixed by @@ .

class Shape 
  @@no_of_shapes = 6

  def instance_method_x
    puts "No: #{@@no_of_shapes}"
  end 

  class << self 
    def class_method_x
      puts "No: #{@@no_of_shapes}"
    end 
  end 
end

They are visible to class methods.

Shape.class_method_x # => No: 6

They are visible to instance methods.

Shape.new.instance_method_x # => No: 6

They cannot be accessed by instance of class.

shape = Shape.new 
puts shape.no_of_shapes 
#=> class_var.rb:5:in `<main>': undefined method `no_of_shapes' for #<Shape:0x000000011e968498> (NoMethodError)
Ruby