Self keyword behavior in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of self inside instance method

What is the output of this Ruby code?

Ruby

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

  def show_self
    puts self
  end
end

p = Person.new("Alice")
p.show_self

A Alice

B #<Person:0x00007fffe30b8c10>

C Person

D self

💡 Hint

Inside an instance method, self refers to the current object instance.

In Ruby, inside an instance method, self refers to the current object instance. Printing self shows the object's default string representation, which includes the class name and an object id.

❓ Predict Output

intermediate

Output of self inside class method

What will this Ruby code print?

Ruby

class Car
  def self.show_self
    puts self
  end
end

Car.show_self

A Car

B #<Car:0x00007fffe30b8c10>

C Object

D self

💡 Hint

Inside a class method, self refers to the class itself.

In Ruby, inside a class method, self refers to the class object. So printing self prints the class name.

🔧 Debug

advanced

Why does this code raise an error?

This Ruby code raises an error. What is the cause?

Ruby

class Animal
  def self.describe
    puts "This is an animal"
    puts self.name
  end

  def name
    "Generic Animal"
  end
end

Animal.describe

A self.name calls a class method 'name' which is not defined, causing NoMethodError

B Instance method 'name' is called correctly, no error

C Syntax error due to missing 'end' keyword

D self refers to an instance, but no instance exists

💡 Hint

Check if 'name' is defined as a class method or instance method.

The method describe is a class method, so self inside it refers to the class Animal. The call self.name tries to call a class method name, but only an instance method name is defined. This causes a NoMethodError.

🧠 Conceptual

advanced

Meaning of self in module method

In Ruby, inside a module method defined with def self.method_name, what does self refer to?

A The class that includes the module

B An instance of the module

C The module object itself

D The main Object

💡 Hint

Modules are objects too in Ruby.

In Ruby, modules are objects of class Module. Inside a module method defined as def self.method_name, self refers to the module object itself.

❓ Predict Output

expert

Output of self in nested context

What does this Ruby code print?

Ruby

class Outer
  def self.show
    puts self
    class Inner
      def self.show_inner
        puts self
      end
    end
    Inner.show_inner
  end
end

Outer.show

A

Outer::Inner
Outer

B

Outer
Inner

C

Outer
self

D

Outer
Outer::Inner

💡 Hint

Check what self refers to in each class method.

In Outer.show, self is Outer. Inside Inner.show_inner, self is Outer::Inner, the nested class's name.