To_s method for string representation in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using to_s?

Consider the following Ruby code:

class Item
  def initialize(name, price)
    @name = name
    @price = price
  end

  def to_s
    "Item: #{@name}, Price: $#{@price}"  
  end
end

item = Item.new("Book", 15)
puts item.to_s

What will be printed?

Ruby

class Item
  def initialize(name, price)
    @name = name
    @price = price
  end

  def to_s
    "Item: #{@name}, Price: $#{@price}"  
  end
end

item = Item.new("Book", 15)
puts item.to_s

A Item: Book, Price: $15

B #<Item:0x00007fffe30b8c20>

C Book 15

D Item Book 15

💡 Hint

Remember, to_s returns a string representation of the object.

The to_s method is overridden to return a formatted string showing the name and price. So puts item.to_s prints Item: Book, Price: $15.

❓ Predict Output

intermediate

What does this to_s method output for a custom class?

Look at this Ruby code:

class Person
  def initialize(name, age)
    @name = name
    @age = age
  end

  def to_s
    "#{@name} is #{@age} years old"
  end
end

p = Person.new("Alice", 30)
puts p

What will be printed?

Ruby

class Person
  def initialize(name, age)
    @name = name
    @age = age
  end

  def to_s
    "#{@name} is #{@age} years old"
  end
end

p = Person.new("Alice", 30)
puts p

A Person: Alice, 30

B #<Person:0x00007fffe30b8c20>

C Alice is 30 years old

D Alice 30

💡 Hint

When you puts an object, Ruby calls to_s automatically.

The to_s method returns a string describing the person. So puts p prints Alice is 30 years old.

🔧 Debug

advanced

Why does this to_s method cause an error?

Examine this Ruby code:

class Product
  def initialize(name, price)
    @name = name
    @price = price
  end

  def to_s
    "Product: #{@name}, Price: $#{price}"
  end
end

p = Product.new("Pen", 2)
puts p.to_s

What error will this code raise?

Ruby

class Product
  def initialize(name, price)
    @name = name
    @price = price
  end

  def to_s
    "Product: #{@name}, Price: $#{price}"
  end
end

p = Product.new("Pen", 2)
puts p.to_s

A NameError: undefined local variable or method `price' for #<Product:0x00007fffe30b8c20>

B SyntaxError: unexpected end-of-input

C TypeError: no implicit conversion of Integer into String

D NoMethodError: undefined method `to_s' for Product

💡 Hint

Check variable names inside string interpolation.

The to_s method uses #{price} but price is not defined as a local variable or method. It should be #{@price}. This causes a NameError.

🧠 Conceptual

advanced

What is the purpose of overriding to_s in Ruby classes?

Why do Ruby programmers override the to_s method in their classes?

A To change the class name of the object

B To provide a meaningful string representation of the object for printing or logging

C To prevent the object from being converted to a string

D To automatically save the object to a file

💡 Hint

Think about what puts object shows by default.

Overriding to_s lets you control what string appears when the object is printed or converted to a string. This helps make output clearer and more useful.

❓ Predict Output

expert

What is the output of this Ruby code with nested to_s calls?

Analyze this Ruby code:

class Point
  def initialize(x, y)
    @x = x
    @y = y
  end

  def to_s
    "(#{@x}, #{@y})"
  end
end

class Line
  def initialize(start_point, end_point)
    @start_point = start_point
    @end_point = end_point
  end

  def to_s
    "Line from #{@start_point.to_s} to #{@end_point.to_s}"
  end
end

p1 = Point.new(1, 2)
p2 = Point.new(3, 4)
line = Line.new(p1, p2)
puts line.to_s

What will be printed?

Ruby

class Point
  def initialize(x, y)
    @x = x
    @y = y
  end

  def to_s
    "(#{@x}, #{@y})"
  end
end

class Line
  def initialize(start_point, end_point)
    @start_point = start_point
    @end_point = end_point
  end

  def to_s
    "Line from #{@start_point.to_s} to #{@end_point.to_s}"
  end
end

p1 = Point.new(1, 2)
p2 = Point.new(3, 4)
line = Line.new(p1, p2)
puts line.to_s

A Line from #<Point:0x00007fffe30b8c20> to #<Point:0x00007fffe30b8c10>

B Line from 1, 2 to 3, 4

C (1, 2) to (3, 4)

D Line from (1, 2) to (3, 4)

💡 Hint

Each to_s returns a string, so nested calls build the full string.

The Line class's to_s calls to_s on its Point objects, which return coordinates in parentheses. So the output is Line from (1, 2) to (3, 4).