Inherited hook in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a method that runs when a subclass is created.

Ruby

class Parent
  def self.[1](subclass)
    puts "A new subclass: #{subclass}"
  end
end

Drag options to blanks, or click blank then click option'

Ainherited

Binitialize

Cnew

Dsubclass_created

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance methods like initialize instead of class methods.

Trying to use a method name that does not exist in Ruby hooks.

The inherited method is a special hook in Ruby that is called when a subclass is created.

2fill in blank

medium

Complete the code to call the inherited hook when a subclass is defined.

Ruby

class Parent
  def self.inherited(subclass)
    puts "Subclass created: [1]"
  end
end

class Child < Parent
end

Drag options to blanks, or click blank then click option'

AChild

Bsubclass

Cself

DParent

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name directly instead of the parameter.

Using self which refers to the parent class.

The subclass parameter in the inherited method refers to the new subclass being created.

3fill in blank

hard

Fix the error in the inherited hook to properly call the parent method.

Ruby

class Parent
  def self.inherited(subclass)
    [1]
    puts "Subclass: #{subclass}"
  end
end

Drag options to blanks, or click blank then click option'

Asuper(subclass)

Bsuper()

Csuperclass

Dsuperclass(subclass)

Attempts:

3 left

💡 Hint

Common Mistakes

Calling super without arguments when the parent method expects one.

Using superclass which is not a method call.

Calling super(subclass) ensures the parent class's inherited method is called with the subclass argument.

4fill in blank

hard

Fill both blanks to create a subclass that triggers the inherited hook and prints its name.

Ruby

class Parent
  def self.inherited(subclass)
    puts "New subclass: [1]"
  end
end

class [2] < Parent
end

Drag options to blanks, or click blank then click option'

Asubclass

BChild

CParent

Dinherited

Attempts:

3 left

💡 Hint

Common Mistakes

Using the parent class name instead of the subclass name.

Not matching the subclass name in the class definition.

The subclass parameter holds the subclass name, and Child is the subclass defined.

5fill in blank

hard

Fill all three blanks to extend the inherited hook to track subclasses in a list.

Ruby

class Parent
  @subclasses = []

  def self.inherited(subclass)
    [1] << [2]
    puts "Tracking subclass: #{subclass}"
  end

  def self.[3]
    @subclasses
  end
end

Drag options to blanks, or click blank then click option'

A@subclasses

Bsubclass

Csubclasses

Dinherited

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance variables instead of class instance variables.

Not defining a method to return the subclasses list.

The class instance variable @subclasses stores subclasses. The method subclasses returns the list.

Practice

1. What does the inherited hook method do in Ruby?

easy

A. It is called automatically when a subclass is created.

B. It runs when an instance of a class is created.

C. It is used to define class variables.

D. It is called when a method is overridden.

Solution

1. Step 1: Understand the purpose of inherited

   The inherited method is a special hook in Ruby that triggers when a subclass is created from a parent class.

2. Step 2: Differentiate from other hooks

   It is not related to instance creation, method overriding, or variable definition, but specifically to subclass creation.

3. Final Answer:

   It is called automatically when a subclass is created. -> Option A

4. Quick Check:

   Inherited hook = called on subclass creation [OK]

Hint: Inherited hook triggers only on subclass creation [OK]

Common Mistakes:

• Confusing inherited with initialize method
• Thinking it runs on instance creation
• Mixing it with method override hooks

2. Which of the following is the correct way to define an inherited hook in a Ruby class?

easy

A. def self.inherited; puts "New subclass created"; end

B. def inherited(self); puts "New subclass created"; end

C. def inherited(subclass); puts "New subclass created"; end

D. def self.inherited(subclass); puts "New subclass created"; end

Solution

1. Step 1: Recognize the method signature

   The inherited hook must be defined as a class method, so it needs self.inherited and takes one argument: the subclass.

2. Step 2: Check method parameters and syntax

   def self.inherited(subclass); puts "New subclass created"; end correctly defines the class method with the subclass parameter. Incorrect versions lack self. (instance method), omit the subclass parameter, or use wrong parameters like self.

3. Final Answer:

   def self.inherited(subclass); puts "New subclass created"; end -> Option D

4. Quick Check:

   Class method with subclass param = def self.inherited(subclass); puts "New subclass created"; end [OK]

Hint: Inherited hook is a class method with subclass param [OK]

Common Mistakes:

• Defining inherited as instance method
• Omitting the subclass parameter
• Forgetting self. for class method

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

class Parent
  def self.inherited(subclass)
    puts "Subclass: #{subclass}"
  end
end

class Child < Parent
end

medium

A. No output

B. Subclass: Child

C. Subclass: Parent

D. SyntaxError

Solution

1. Step 1: Understand when inherited runs

   The inherited method in Parent runs automatically when a subclass is created.

2. Step 2: Identify subclass creation

   When Child < Parent is declared, Parent.inherited(Child) is called, printing "Subclass: Child".

3. Final Answer:

   Subclass: Child -> Option B

4. Quick Check:

   Subclass creation triggers inherited hook output [OK]

Hint: Inherited prints subclass name on subclass creation [OK]

Common Mistakes:

• Expecting output on instance creation
• Confusing subclass with parent class name
• Thinking no output occurs

4. Identify the error in this Ruby code using the inherited hook:

class Base
  def inherited(subclass)
    puts "Subclass created: #{subclass}"
  end
end

class Derived < Base
end

medium

A. The inherited method should be a class method with self.

B. The subclass parameter is missing.

C. The puts statement syntax is incorrect.

D. Derived class should not inherit from Base.

Solution

1. Step 1: Check method definition context

   The inherited hook must be a class method, so it requires def self.inherited(subclass).

2. Step 2: Identify the error in the code

   Here, inherited is defined as an instance method, missing self., so it won't be called on subclass creation.

3. Final Answer:

   The inherited method should be a class method with self. -> Option A

4. Quick Check:

   Inherited hook must be class method [OK]

Hint: Inherited must be defined with self. to work [OK]

Common Mistakes:

• Defining inherited as instance method
• Omitting self. in method definition
• Misunderstanding inherited hook usage

5. How can you use the inherited hook to automatically add a class variable @@subclasses that tracks all subclasses of a parent class?

hard

A. Use initialize method to track subclasses in @@subclasses.

B. Define an instance method inherited to add subclass to @@subclasses.

C. Define self.inherited(subclass) to append subclass to @@subclasses array.

D. Manually add subclasses to @@subclasses outside the class.

Solution

1. Step 1: Understand subclass tracking

   To track subclasses, use a class variable @@subclasses initialized as an array in the parent class.

2. Step 2: Use inherited hook to update tracking

   Define self.inherited(subclass) to append the new subclass to @@subclasses automatically when a subclass is created.

3. Final Answer:

   Define self.inherited(subclass) to append subclass to @@subclasses array. -> Option C

4. Quick Check:

   Inherited hook + class variable tracks subclasses [OK]

Hint: Use inherited hook to update subclass list automatically [OK]

Common Mistakes:

• Using instance methods to track subclasses
• Tracking subclasses in initialize method
• Forgetting to initialize @@subclasses as array