Instance_variable_get and set in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using instance_variable_get?

Consider the following Ruby class and code. What will be printed when this code runs?

Ruby

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

p = Person.new("Alice")
puts p.instance_variable_get(:@name)

A nil

B Error: undefined method `instance_variable_get' for Person

C Alice

D @name

💡 Hint

instance_variable_get reads the value of an instance variable by its name symbol.

The instance_variable_get method returns the value of the instance variable named by the symbol. Here, @name holds "Alice", so it prints Alice.

❓ Predict Output

intermediate

What does this code print after using instance_variable_set?

Look at this Ruby code. What will be the output?

Ruby

class Car
  def initialize
    @speed = 0
  end
end

car = Car.new
car.instance_variable_set(:@speed, 100)
puts car.instance_variable_get(:@speed)

A 100

B 0

C nil

D Error: undefined method `instance_variable_set' for Car

💡 Hint

instance_variable_set changes the value of an instance variable.

The instance_variable_set method sets the value of @speed to 100. Then instance_variable_get returns 100, which is printed.

❓ Predict Output

advanced

What error does this code raise?

What error will this Ruby code produce when run?

Ruby

class Box
  def initialize
    @content = "secret"
  end
end

box = Box.new
box.instance_variable_get("content")

A No error, returns nil

B NameError

C ArgumentError

D TypeError

💡 Hint

instance_variable_get expects a symbol or string starting with @.

instance_variable_get requires the variable name to start with '@'. Passing "content" without '@' causes a TypeError.

❓ Predict Output

advanced

What is the output of this code using instance_variable_set dynamically?

What will this Ruby code print?

Ruby

class User
  def initialize
    @data = {}
  end
  def set_var(name, value)
    instance_variable_set("@" + name.to_s, value)
  end
  def get_var(name)
    instance_variable_get("@" + name.to_s)
  end
end

user = User.new
user.set_var(:age, 30)
puts user.get_var(:age)

A age

B 30

C nil

D Error: undefined method `set_var' for User

💡 Hint

instance_variable_set and get can use string names with '@' prefix.

The set_var method sets @age to 30. The get_var method retrieves @age, printing 30.

🧠 Conceptual

expert

How many instance variables does this object have after running the code?

After running this Ruby code, how many instance variables does the object 'obj' have?

Ruby

class Sample
  def initialize
    @a = 1
    @b = 2
  end
end

obj = Sample.new
obj.instance_variable_set(:@c, 3)
obj.instance_variable_set(:@d, 4)
obj.instance_variable_get(:@a)
obj.instance_variable_get(:@b)

A 4

B 2

C 3

D 5

💡 Hint

instance_variable_set adds new instance variables if they don't exist.

Initially, obj has @a and @b. Then @c and @d are added by instance_variable_set. So total 4 instance variables.