Ruby Accessors

An accessor is a method that lets outside code read or change a value stored inside an object. The attr lines write accessor methods for a class.

A stored name stays hidden

The dog stores its name in @name. respond_to? asks if the object answers to name, and it prints false because no reader exists yet.

class Dog
  def initialize(name)
    @name = name
  end
end
dog = Dog.new("Rex")
puts dog.respond_to?(:name)

A hand-written reader

The name method inside the class gives @name to outside code. respond_to? prints true now, and the name itself prints.

class Dog
  def initialize(name)
    @name = name
  end
  def name
    @name
  end
end
dog = Dog.new("Rex")
puts dog.respond_to?(:name)
puts dog.name

attr_reader writes the reader

attr_reader :name writes the same reader method for the class. The two printed lines match the hand-written version.

class Dog
  attr_reader :name
  def initialize(name)
    @name = name
  end
end
dog = Dog.new("Rex")
puts dog.respond_to?(:name)
puts dog.name

attr_writer sets a new name

attr_writer :name writes a method that sets @name from outside. The greet line shows the new name after the change.

class Dog
  attr_writer :name
  def initialize(name)
    @name = name
  end
  def greet
    puts "#{@name} says hello"
  end
end
dog = Dog.new("Rex")
dog.name = "Max"
dog.greet

attr_accessor does both jobs

attr_accessor :name writes the reader and the writer in one line. The name prints, changes, and prints again.

class Dog
  attr_accessor :name
  def initialize(name)
    @name = name
  end
end
dog = Dog.new("Rex")
puts dog.name
dog.name = "Max"
puts dog.name

Example

class Dog
  attr_accessor :name
  attr_accessor :age
  def initialize(name, age)
    @name = name
    @age = age
  end
  def profile
    puts "#{@name} is #{@age} years old"
  end
end
dog = Dog.new("Rex", 3)
puts dog.name
dog.age = 4
dog.profile

Key points

A value in @name stays hidden from outside code until a method shares it.
A reader is a method that gives outside code a stored value.
attr_reader writes a reader method for the named value.
attr_writer writes a writer method for the named value.
attr_accessor writes both a reader and a writer.
A writer call looks like a plain assignment, as in dog.name = "Max".

In this example, attr_accessor lines give Dog a reader and a writer for name and age. The first print reads the name through the reader. Setting age to 4 uses the writer, and profile shows the new age.

Note

The name after an attr word is a symbol, like :name.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz Ruby Compiler

class Dog
  attr_accessor :name
  attr_accessor :age
  def initialize(name, age)
    @name = name
    @age = age
  end
  def profile
    puts "#{@name} is #{@age} years old"
  end
end
dog = Dog.new("Rex", 3)
puts dog.name
dog.age = 4
dog.profile

Exercise

Which line writes both a reader and a writer for name?

attr_accessor :name attr_reader :name attr_writer :name attr_both :name