Extend for class methods in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a module method that can be used as a class method.

Ruby

module Greetings
  def [1](name)
    "Hello, #{name}!"
  end
end

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

Amodule.say_hello

Bself.say_hello

Csay_hello

Ddef say_hello

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 'self.' inside the module method definition.

The method inside the module is defined normally. To use it as a class method, it will be extended later.

2fill in blank

medium

Complete the code to extend the module as class methods in the class.

Ruby

class Person
  extend [1]
end

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

AGreetings

Bself.Greetings

Cinclude Greetings

Dmodule Greetings

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'include' instead of 'extend'.

Using extend Greetings adds the module methods as class methods to Person.

3fill in blank

hard

Fix the error in calling the class method from the module.

Ruby

puts Person.[1]("Alice")

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

AsayHello

BGreetings.say_hello

Csay_hello

Dself.say_hello

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the method with module prefix or wrong method name.

The class method is called directly on the class with the method name defined in the module.

4fill in blank

hard

Fill both blanks to define and extend a module with a class method.

Ruby

module Logger
  def [1](msg)
    puts "Log: #{msg}"
  end
end

class App
  [2] Logger
end

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

Alog

Binclude

Cextend

Ddef

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'include' instead of 'extend' for class methods.

Define the method 'log' in the module and use 'extend' to add it as a class method to App.

5fill in blank

hard

Fill all three blanks to create a module with a class method and call it.

Ruby

module Utils
  def [1](value)
    value * 2
  end
end

class Calculator
  [2] Utils
end

result = Calculator.[3](5)
puts result

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

Adouble

Bextend

Dinclude

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'include' instead of 'extend' for class methods.

The method 'double' is defined in the module. The class extends the module to get class methods. Then the method is called on the class.

Practice

1. What does the extend keyword do in Ruby when used inside a class?

easy

A. Includes the module's constants only

B. Adds the module's methods as instance methods to the class

C. Adds the module's methods as class methods to the class

D. Removes methods from the class

Solution

1. Step 1: Understand extend usage

   The extend keyword adds methods from a module as class methods to the class that calls it.

2. Step 2: Differentiate from include

   Unlike include, which adds methods as instance methods, extend adds them as class methods.

3. Final Answer:

   Adds the module's methods as class methods to the class -> Option C

4. Quick Check:

   extend = class methods [OK]

Hint: Remember: extend = class methods, include = instance methods [OK]

Common Mistakes:

• Confusing extend with include
• Thinking extend adds instance methods
• Assuming extend removes methods

2. Which of the following is the correct syntax to add module methods as class methods using extend?

easy

A. class MyClass; def self.extend MyModule; end

B. class MyClass; include MyModule; end

C. class MyClass; MyModule.extend(self); end

D. class MyClass; extend MyModule; end

Solution

1. Step 1: Identify correct extend usage

   The correct syntax is to call extend inside the class body with the module name.

2. Step 2: Check each option

   class MyClass; extend MyModule; end uses extend MyModule inside the class, which is correct syntax.

3. Final Answer:

   class MyClass; extend MyModule; end -> Option D

4. Quick Check:

   Correct extend syntax = class MyClass; extend MyModule; end [OK]

Hint: Use 'extend ModuleName' inside class body for class methods [OK]

Common Mistakes:

• Using include instead of extend
• Calling extend on module instead of class
• Incorrect method definition syntax

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

module Greetings
  def hello
    "Hello from module"
  end
end

class Person
  extend Greetings
end

puts Person.hello

medium

A. NoMethodError: undefined method 'hello' for Person

B. Hello from module

C. Hello from module called on instance

D. SyntaxError

Solution

1. Step 1: Understand extend Greetings effect

   The module's method hello becomes a class method of Person.

2. Step 2: Check method call

   Person.hello calls the class method, which exists and returns "Hello from module".

3. Final Answer:

   Hello from module -> Option B

4. Quick Check:

   Class method from extend = "Hello from module" [OK]

Hint: extend adds module methods as class methods, so Person.hello works [OK]

Common Mistakes:

• Thinking hello is an instance method
• Calling hello on an instance instead of class
• Expecting NoMethodError

4. Identify the error in this Ruby code snippet:

module Tools
  def tool_name
    "Hammer"
  end
end

class Worker
  extend Tools

  def self.tool_name
    "Wrench"
  end
end

puts Worker.tool_name

medium

A. No error; output is 'Wrench'

B. NoMethodError because tool_name is undefined

C. SyntaxError due to extend usage

D. Output is 'Hammer' ignoring class method

Solution

1. Step 1: Analyze method definitions

   The module Tools defines tool_name, which is added as a class method to Worker by extend Tools.

2. Step 2: Check method override

   Worker defines its own class method tool_name, which overrides the module method.

3. Final Answer:

   No error; output is 'Wrench' -> Option A

4. Quick Check:

   Class method override works; output = 'Wrench' [OK]

Hint: Class methods override extended module methods if defined later [OK]

Common Mistakes:

• Assuming module method overrides class method
• Expecting NoMethodError
• Confusing instance and class methods

5. You want to share a method info as a class method across multiple classes without repeating code. Which approach using extend is best?

module InfoModule
  def info
    "Shared class info"
  end
end

class Alpha
  # What to do here?
end

class Beta
  # What to do here?
end

hard

A. Add extend InfoModule inside both Alpha and Beta classes

B. Add include InfoModule inside both Alpha and Beta classes

C. Define def self.info separately in Alpha and Beta

D. Use InfoModule.extend(self) outside classes

Solution

1. Step 1: Understand sharing class methods

   Using extend InfoModule inside each class adds info as a class method.

2. Step 2: Evaluate options

   Add extend InfoModule inside both Alpha and Beta classes correctly uses extend in both classes to share the method without repetition.

3. Final Answer:

   Add extend InfoModule inside both Alpha and Beta classes -> Option A

4. Quick Check:

   Use extend in each class to share class methods [OK]

Hint: Use extend inside each class to share class methods from a module [OK]

Common Mistakes:

• Using include instead of extend for class methods
• Defining methods separately instead of sharing
• Calling extend on module instead of class