Attr_reader, attr_writer, attr_accessor in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using attr_reader?

Consider this Ruby class with attr_reader. What will be printed?

Ruby

class Person
  attr_reader :name
  def initialize(name)
    @name = name
  end
end

p = Person.new("Alice")
puts p.name
p.name = "Bob"

A

Alice
Bob

B NoMethodError: undefined method `name' for #<Person:...>

C

Alice
NoMethodError: undefined method `name=' for #<Person:...>

D

nil
NoMethodError: undefined method `name=' for #<Person:...>

💡 Hint

Remember, attr_reader creates a getter method but no setter.

attr_reader creates a method to read the instance variable but does not allow writing. So p.name works and prints "Alice". But p.name = "Bob" raises a NoMethodError because the setter method is missing.

❓ Predict Output

intermediate

What happens when using attr_writer only?

Look at this Ruby code using attr_writer. What will be the output or error?

Ruby

class Car
  attr_writer :color
  def initialize(color)
    @color = color
  end
end

car = Car.new("red")
puts car.color
car.color = "blue"
puts car.instance_variable_get(:@color)

A NoMethodError: undefined method `color' for #<Car:...>

B NoMethodError: undefined method `color=' for #<Car:...>

C

nil
blue

D

red
blue

💡 Hint

attr_writer creates a setter but no getter method.

attr_writer creates a setter method color= but no getter color. So car.color raises NoMethodError. The setter car.color = "blue" works and changes the instance variable. Using instance_variable_get shows the updated value.

❓ Predict Output

advanced

What is the output when using attr_accessor?

Given this Ruby class with attr_accessor, what will be printed?

Ruby

class Book
  attr_accessor :title
  def initialize(title)
    @title = title
  end
end

book = Book.new("Ruby 101")
puts book.title
book.title = "Ruby 102"
puts book.title

A

Ruby 101
Ruby 102

B

Ruby 101
Ruby 101

C NoMethodError: undefined method `title=' for #<Book:...>

D NoMethodError: undefined method `title' for #<Book:...>

💡 Hint

attr_accessor creates both getter and setter methods.

attr_accessor creates both title and title= methods. So you can read and write the @title instance variable. The output shows the original title and the updated title.

🧠 Conceptual

advanced

Which statement about attr_reader, attr_writer, and attr_accessor is true?

Choose the correct statement about these Ruby attribute methods.

A <code>attr_reader</code> creates both getter and setter methods.

B <code>attr_accessor</code> creates getter and setter methods.

C <code>attr_writer</code> creates only a getter method.

D <code>attr_accessor</code> creates only a setter method.

💡 Hint

Think about which methods allow reading and writing.

attr_reader creates only getter methods. attr_writer creates only setter methods. attr_accessor creates both getter and setter methods.

🔧 Debug

expert

Why does this Ruby code raise NoMethodError when using attr_writer?

Look at this code snippet. Why does puts user.name raise NoMethodError?

Ruby

class User
  attr_writer :name
  def initialize(name)
    @name = name
  end
end

user = User.new("Eve")
puts user.name

A Because <code>attr_writer</code> creates only a getter method, no setter method exists.

B Because <code>attr_writer</code> creates both getter and setter methods, but the getter is private.

C Because the instance variable <code>@name</code> is not initialized.

D Because <code>attr_writer</code> only creates a setter method, no getter method exists.

💡 Hint

Check what methods attr_writer creates.

attr_writer creates only the setter method name=. It does not create a getter method name. So calling user.name raises NoMethodError.