Attr_reader, attr_writer, attr_accessor in Ruby - Mini Project: Build & Apply

Using attr_reader, attr_writer, and attr_accessor in Ruby

📖 Scenario: Imagine you are creating a simple program to manage a book's information in a library system. You want to control how the book's title and author can be accessed and changed.

🎯 Goal: Build a Ruby class Book that uses attr_reader, attr_writer, and attr_accessor to manage the book's title and author attributes properly.

📋 What You'll Learn

Create a class called Book with two instance variables: @title and @author.

Use attr_reader to allow reading the title only.

Use attr_writer to allow writing (changing) the author only.

Use attr_accessor to allow both reading and writing for a new attribute publisher.

Create an instance of Book with initial values for title, author, and publisher.

Print the title, change the author, change the publisher, and print all updated values.

💡 Why This Matters

🌍 Real World

Using <code>attr_reader</code>, <code>attr_writer</code>, and <code>attr_accessor</code> helps control how data inside objects can be accessed or changed, which is important in real software to keep data safe and consistent.

💼 Career

Many Ruby jobs require understanding how to use these accessors to write clean, maintainable code that protects object data and follows good design principles.

1

Create the Book class with instance variables

Create a class called Book with an initialize method that sets @title to "Ruby Basics" and @author to "Jane Doe".

Ruby

# Define the Book class and initialize method
# Your code here

Hint

Use class Book and define initialize with @title and @author set to the exact strings.

2

Add attr_reader and attr_writer for title and author

Add attr_reader :title to allow reading the title and attr_writer :author to allow changing the author.

Ruby

class Book
  def initialize
    @title = "Ruby Basics"
    @author = "Jane Doe"
  end

# Add attr_reader for title and attr_writer for author
# Your code here

Hint

Use attr_reader :title and attr_writer :author inside the class but outside any method.

3

Add attr_accessor for publisher and initialize it

Add attr_accessor :publisher to the class and update the initialize method to set @publisher to "Tech Books Publishing".

Ruby

class Book
  attr_reader :title
  attr_writer :author

  def initialize
    @title = "Ruby Basics"
    @author = "Jane Doe"
    # Initialize @publisher here
  end

# Add attr_accessor for publisher
# Your code here

Hint

Add attr_accessor :publisher and set @publisher in initialize.

4

Create a Book instance and use the accessors

Create a variable book as a new Book instance. Print the title using book.title. Change the author to "John Smith" using book.author=. Change the publisher to "New Publisher" using book.publisher=. Finally, print the updated author and publisher using puts.

Ruby

book = Book.new
# Print the title
# Change author to "John Smith"
# Change publisher to "New Publisher"
# Print updated author and publisher
# Your code here

Hint

Create the book object, print title, update author and publisher, then print updated values.

Practice

1. What does attr_reader do in a Ruby class?

easy

A. Creates a method to read an attribute value

B. Creates a method to write an attribute value

C. Creates methods to both read and write an attribute

D. Deletes an attribute from the class

Solution

1. Step 1: Understand attr_reader purpose

   attr_reader defines a getter method for an instance variable, allowing you to read its value.

2. Step 2: Compare with other attr methods

   attr_writer creates a setter (write) method, and attr_accessor creates both getter and setter methods.

3. Final Answer:

   Creates a method to read an attribute value -> Option A

4. Quick Check:

   attr_reader = read method [OK]

Hint: attr_reader = read only method [OK]

Common Mistakes:

• Confusing attr_reader with attr_writer
• Thinking attr_reader allows writing values
• Mixing attr_accessor with attr_reader

2. Which of the following is the correct syntax to create both getter and setter methods for @name in Ruby?

easy

A. attr_writer :name

B. attr_accessor :name

C. attr_reader :name

D. attr_both :name

Solution

1. Step 1: Recall attr_accessor usage

   attr_accessor creates both getter and setter methods for the given symbol.

2. Step 2: Check other options

   attr_reader only creates getter, attr_writer only setter, and attr_both is invalid syntax.

3. Final Answer:

   attr_accessor :name -> Option B

4. Quick Check:

   attr_accessor = read + write [OK]

Hint: Use attr_accessor for read and write [OK]

Common Mistakes:

• Using attr_reader when write is needed
• Using invalid method names like attr_both
• Confusing attr_writer with attr_accessor

3. What will be the output of this Ruby code?

class Person
  attr_writer :age
  def initialize(age)
    @age = age
  end
  def show_age
    @age
  end
end

p = Person.new(30)
puts p.show_age
p.age = 40
puts p.show_age

medium

A. 30\n40

B. 30\n30

C. Error: undefined method `age='

D. Error: undefined method `show_age'

Solution

1. Step 1: Understand attr_writer effect

   attr_writer :age creates a setter method age=, but no getter method is created.

2. Step 2: Analyze method calls

   p.show_age returns @age which is 30 initially. Then p.age = 40 sets @age to 40. But p.show_age returns @age which is now 40.

3. Step 3: Check output

   Actually, p.show_age is called twice, before and after setting age. So outputs are 30 then 40.

4. Final Answer:

   30\n40 -> Option A

5. Quick Check:

   attr_writer allows setting, show_age reads @age [OK]

Hint: attr_writer only sets; custom getter needed [OK]

Common Mistakes:

• Assuming attr_writer creates getter method
• Expecting error on p.age= assignment
• Confusing show_age method with attr_reader

4. Identify the error in this Ruby class:

class Car
  attr_reader :model
  def initialize(model)
    @model = model
  end
  def model=(value)
    @model = value
  end
end

car = Car.new('Sedan')
car.model = 'SUV'
puts car.model

medium

A. Error: attr_reader conflicts with manual setter method

B. Error: undefined method 'model='

C. Error: attr_reader does not create setter method

D. No error, code runs and prints 'SUV'

Solution

1. Step 1: Check attr_reader and setter method

   attr_reader :model creates a getter method. The setter method model= is manually defined.

2. Step 2: Analyze method calls

   car.model = 'SUV' calls the manual setter, updating @model. puts car.model calls the getter from attr_reader, printing 'SUV'.

3. Final Answer:

   No error, code runs and prints 'SUV' -> Option D

4. Quick Check:

   attr_reader + manual setter works [OK]

Hint: attr_reader + manual setter is valid [OK]

Common Mistakes:

• Assuming attr_reader creates setter method
• Thinking attr_reader conflicts with manual setter
• Expecting error on model= assignment

5. You want a Ruby class Book where the title can be read but not changed, and the author can be both read and changed. Which attribute methods should you use?

hard

A. attr_writer :title
attr_writer :author

B. attr_writer :title
attr_reader :author

C. attr_reader :title
attr_accessor :author

D. attr_accessor :title
attr_writer :author

Solution

1. Step 1: Determine access for title

   Title should be readable but not writable, so use attr_reader :title.

2. Step 2: Determine access for author

   Author should be readable and writable, so use attr_accessor :author.

3. Final Answer:

   attr_reader :title attr_accessor :author -> Option C

4. Quick Check:

   Read-only + read-write = attr_reader + attr_accessor [OK]

Hint: Use attr_reader for read-only, attr_accessor for read-write [OK]

Common Mistakes:

• Using attr_writer for read-only attribute
• Using attr_accessor for read-only attribute
• Mixing up read and write access