ruby attr_reader attr_writer attr_accessor

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wang xiao bo
·Sep 3, 2021·

2 min read

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In Ruby, we can use attr_reader to give object instances a simpler way to read the class instance variables:

class TeaMaker
    attr_reader :colour, :temperature, :quantity, :origin, :brand
    def initialize(colour,temperature, quantity, origin, brand)
        @colour = colour
        @temperature = temperature
        @quantity = quantity
        @origin = origin
        @brand = brand
    end
end

teat1 = TeaMaker.new("dark", "hot", "small", "China", "puer")
puts tea1.colour // dark
puts tea1.temperature //hot
puts tea1.quantity   // small
puts tea1.origin // China
puts tea1.brand  // puer

Now imagine, that the TeaMaker has not one but five instance variables. For this to work, we’ll have to create 5 methods to provide access to read them and 5 methods to change their respective values. This can quickly become difficult to manage.

In Ruby, we can use attr_writer along with attr_reader to give object instances a simpler way to update the class instance variables:

class TeaMaker
  attr_reader :colour, :temperature, :quantity, :origin, :brand
  attr_writer :colour, :temperature, :quantity, :origin, :brand
  def initialize(colour, temperature, quantity, origin, brand)
    @colour = colour
    @temperature = temperature
    @quantity = quantity
    @origin = origin
    @brand = brand
  end
end

tea1 = TeaMaker.new("dark", "hot", "small", "Brunei", "Domos")
tea1.colour = "light"
puts tea1.colour
tea1.temperature = "cold"
puts tea1.temperature
tea1.quantity = "large"
puts tea1.quantity
tea1.origin = "nochina"
puts tea1.origin
tea1.brand = "longjin"
puts tea1.brand

attr_reader :colour, :temperature, :quantity, :origin, :brand attr_writer :colour, :temperature, :quantity, :origin, :brand it seems like a complicated way to achieve a simple thing: access and change instance variables. Ruby provides us with attr_accessor to simplify this code:

class TeaMaker

  attr_accessor :colour, :temperature, :quantity, :origin, :brand
  def initialize(colour, temperature, quantity, origin, brand)
    @colour = colour
    @temperature = temperature
    @quantity = quantity
    @origin = origin
    @brand = brand
  end
end

tea1 = TeaMaker.new("dark", "hot", "small", "Brunei", "Domos")
tea1.colour = "light"
puts tea1.colour
tea1.temperature = "cold"
puts tea1.temperature
tea1.quantity = "large"
puts tea1.quantity
tea1.origin = "nochina"
puts tea1.origin
tea1.brand = "longjin"
puts tea1.brand
 
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