Module declaration syntax in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of module method call

What is the output of this Ruby code?

Ruby

module Greetings
  def self.say_hello
    "Hello from module!"
  end
end

puts Greetings.say_hello

A Hello from module!

B SyntaxError

C NoMethodError

D nil

💡 Hint

Look at how the method is defined with self inside the module.

The method say_hello is defined as a module method using self. Calling Greetings.say_hello prints the string.

❓ Predict Output

intermediate

Output of including a module

What will be printed when this Ruby code runs?

Ruby

module Talk
  def speak
    "I can talk"
  end
end

class Person
  include Talk
end

puts Person.new.speak

A SyntaxError

B NoMethodError

C I can talk

D nil

💡 Hint

Including a module adds its methods as instance methods.

The module Talk is included in Person, so Person instances can call speak, printing 'I can talk'.

❓ Predict Output

advanced

Output of nested module constants

What is the output of this Ruby code?

Ruby

module Outer
  VALUE = 10
  module Inner
    VALUE = 20
    def self.value
      VALUE
    end
  end
end

puts Outer::Inner.value

A nil

B 20

C NameError

D 10

💡 Hint

Constants inside nested modules are accessed by their own scope.

Inner module has its own VALUE constant set to 20. The method returns Inner::VALUE, which is 20.

❓ Predict Output

advanced

Error raised by invalid module syntax

What error does this Ruby code raise?

Ruby

module Sample
  def method
    puts "Hello"
  # missing end here

A SyntaxError

B RuntimeError

C NameError

D NoMethodError

💡 Hint

Check if all blocks and modules are properly closed.

The module and method definitions are not closed with 'end', causing a SyntaxError.

🧠 Conceptual

expert

Number of methods available after module inclusion

Given this Ruby code, how many methods can be called on an instance of class C?

Ruby

module M1
  def a; 1; end
end

module M2
  def b; 2; end
end

class C
  include M1
  include M2
  def c; 3; end
end

obj = C.new

A 0

B 2

C 1

D 3

💡 Hint

Including modules adds their instance methods to the class.

Class C has method c and includes M1 and M2, adding methods a and b. So obj has 3 methods: a, b, c.

Practice

1. What is the correct way to declare a module named MathTools in Ruby?

easy

A. def MathTools
# code here
end

B. module MathTools
# code here
end

C. class MathTools
# code here
end

D. package MathTools {
# code here
}

Solution

1. Step 1: Recognize Ruby module syntax

   In Ruby, modules are declared using the keyword module followed by the module name and end.

2. Step 2: Identify the correct declaration

   module MathTools # code here end uses module MathTools ... end, which is the correct syntax for a module.

3. Final Answer:

   module MathTools # code here end -> Option B

4. Quick Check:

   Ruby modules use module Name ... end [OK]

Hint: Modules start with 'module' and end with 'end' [OK]

Common Mistakes:

• Using 'class' instead of 'module'
• Using 'def' which is for methods
• Using non-Ruby syntax like 'package'

2. Which of the following is a syntax error when declaring a module in Ruby?

easy

A. module Tools {
def help
end
}

B. module Tools
def self.help
end
end

C. module Tools
end

D. module Tools
CONSTANT = 10
end

Solution

1. Step 1: Check Ruby module block delimiters

   Ruby modules use module ... end without braces { }.

2. Step 2: Identify invalid syntax

   module Tools { def help end } uses braces { } which is invalid syntax for module declaration in Ruby.

3. Final Answer:

   module Tools { def help end } -> Option A

4. Quick Check:

   Ruby modules use 'module ... end', not braces [OK]

Hint: Ruby modules never use curly braces for blocks [OK]

Common Mistakes:

• Using curly braces instead of 'end'
• Missing 'end' keyword
• Confusing module with class syntax

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

module Greetings
  def self.say_hello
    "Hello!"
  end
end

puts Greetings.say_hello

medium

A. Hello!

B. Greetings.say_hello

C. NoMethodError

D. SyntaxError

Solution

1. Step 1: Understand module method definition

   The method say_hello is defined as a module method using self., so it can be called on the module directly.

2. Step 2: Evaluate the method call output

   Calling Greetings.say_hello returns the string "Hello!", which is printed by puts.

3. Final Answer:

   Hello! -> Option A

4. Quick Check:

   Module method call returns string output [OK]

Hint: Module methods use self. and can be called directly [OK]

Common Mistakes:

• Trying to call method without self. prefix
• Expecting instance method behavior
• Confusing syntax errors with method calls

4. Identify the error in the following Ruby module declaration:

module Tools
  def help
    "Help message"
  end
end

Tools.help

medium

A. No error, code runs fine

B. Missing 'end' keyword for module

C. Method 'help' should be defined with 'self.' to call on module

D. Module name should be lowercase

Solution

1. Step 1: Check method definition inside module

   The method help is defined as an instance method, but called on the module directly.

2. Step 2: Understand method call context

   To call Tools.help, help must be a module method defined with self.help.

3. Final Answer:

   Method 'help' should be defined with 'self.' to call on module -> Option C

4. Quick Check:

   Module methods need 'self.' prefix to be called on module [OK]

Hint: Use 'def self.method' for module-level methods [OK]

Common Mistakes:

• Defining instance methods but calling on module
• Forgetting 'self.' prefix for module methods
• Assuming lowercase module names are valid

5. Given the following nested module declarations, which is the correct way to define a module Inner inside module Outer in Ruby?

module Outer
  # Your code here
end

hard

A. module Outer
class Inner
end
end

B. module Outer::Inner
end

C. module Outer.Inner
end

D. module Outer
module Inner
end
end

Solution

1. Step 1: Understand nested module syntax

   In Ruby, nested modules can be declared by placing one module inside another.

2. Step 2: Identify correct nested declaration

   module Outer module Inner end end correctly nests module Inner inside module Outer using indentation and end keywords.

3. Final Answer:

   module Outer module Inner end end -> Option D

4. Quick Check:

   Nested modules use nested 'module ... end' blocks [OK]

Hint: Nest modules by placing one inside another with 'module' [OK]

Common Mistakes:

• Using dot notation instead of :: for nested modules
• Using class instead of module for nested module
• Incorrect syntax like dot (.) in module names