Super keyword behavior in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the super keyword do in Ruby?

The super keyword calls the same method from the parent class, allowing you to extend or reuse the parent's behavior.

intermediate

What happens if you use super without parentheses and arguments inside a method?

Ruby automatically passes all the arguments received by the current method to the parent method when you call super without parentheses.

intermediate

How does super() differ from super in Ruby?

super() calls the parent method without passing any arguments, even if the current method received some.

beginner

Can super be used in methods without a parent method of the same name?

No. Using super in a method without a matching parent method will raise a NoMethodError.

beginner

Why is super useful in object-oriented programming?

super helps reuse and extend code from parent classes, making programs easier to maintain and avoiding duplication.

What does super do when called inside a method?

A Calls the same method from the parent class

B Calls a random method from the parent class

C Calls the method from the child class

D Creates a new method

super calls the same method from the parent class to reuse or extend its behavior.

What happens if you write super() with empty parentheses?

A Calls a different method

B Passes all current method arguments to the parent method

C Raises an error

D Passes no arguments to the parent method

super() calls the parent method without passing any arguments.

If a method receives arguments and you call super without parentheses, what happens?

A No arguments are passed to the parent method

B Only the first argument is passed

C All arguments are passed to the parent method

D An error occurs

Calling super without parentheses passes all current method arguments to the parent method.

What error occurs if super is called but no parent method exists?

A NameError

B NoMethodError

C ArgumentError

D SyntaxError

Ruby raises a NoMethodError if super is called but no matching parent method exists.

Why use super in a child class method?

A To reuse and extend the parent method's behavior

B To call a method from a sibling class

C To delete the parent method

D To ignore the parent method

super allows the child method to reuse and add to the parent method's behavior.

Explain how the super keyword works in Ruby and how it handles arguments.

Think about how Ruby decides what arguments to send when you use super.

Describe a real-life example where using super helps avoid repeating code.

Imagine a recipe where you want to add toppings but keep the base steps.

Practice

1. What does the super keyword do in Ruby?

easy

A. Creates a new instance of the parent class

B. Overrides the parent class's method permanently

C. Calls the parent class's method with the same name

D. Deletes the parent class's method

Solution

1. Step 1: Understand the role of super

   The super keyword is used inside a child class method to call the method with the same name from its parent class. It does not create, override, or delete methods but simply calls the parent method to reuse or extend its behavior.

2. Final Answer:

   Calls the parent class's method with the same name -> Option C

3. Quick Check:

   super calls parent method [OK]

Hint: Remember: super calls parent method with same name [OK]

Common Mistakes:

• Thinking super creates or deletes methods
• Confusing super with instance creation
• Assuming super overrides methods permanently

2. Which of the following is the correct syntax to call the parent method with no arguments using super?

easy

A. super()

B. super[]

C. super

D. super{}

Solution

1. Step 1: Understand super with parentheses

   Using super() calls the parent method explicitly with no arguments, ignoring any current method arguments. Only super() uses parentheses correctly to pass no arguments; other forms are invalid syntax.

2. Final Answer:

   super() -> Option A

3. Quick Check:

   super() means no arguments [OK]

Hint: Use parentheses to call parent with no args: super() [OK]

Common Mistakes:

• Using super without parentheses to mean no arguments
• Using brackets or braces instead of parentheses
• Confusing super() with super without parentheses

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

class Parent
  def greet(name)
    "Hello, #{name} from Parent"
  end
end

class Child < Parent
  def greet(name)
    super + " and Child"
  end
end

puts Child.new.greet("Alice")

medium

A. Hello, Alice from Parent and Child

B. Hello, Alice from Child

C. Hello, from Parent and Child

D. Error: wrong number of arguments

Solution

1. Step 1: Trace the method call in Child#greet

   The Child's greet method calls super without parentheses, so it passes the argument "Alice" to Parent#greet. Parent#greet returns "Hello, Alice from Parent". Child appends " and Child" to this string.

2. Final Answer:

   Hello, Alice from Parent and Child -> Option A

3. Quick Check:

   super passes args, output combines strings [OK]

Hint: super without () passes all args automatically [OK]

Common Mistakes:

• Assuming super passes no arguments by default
• Expecting an error due to argument mismatch
• Ignoring the appended string in Child method

4. Identify the error in this Ruby code:

class Parent
  def initialize(age)
    @age = age
  end
end

class Child < Parent
  def initialize
    super
    @name = "Child"
  end
end

Child.new

medium

A. NameError for @name variable

B. No error, code runs fine

C. SyntaxError due to missing parentheses

D. ArgumentError: wrong number of arguments for super

Solution

1. Step 1: Check Parent initialize method

   Parent's initialize requires one argument age. Child's initialize calls super without arguments, so it tries to call Parent's initialize with zero arguments, causing an ArgumentError.

2. Final Answer:

   ArgumentError: wrong number of arguments for super -> Option D

3. Quick Check:

   super must match parent args or use super() [OK]

Hint: super without args passes current args; mismatch causes error [OK]

Common Mistakes:

• Assuming super() passes parent's required args automatically
• Ignoring that Parent requires an argument
• Thinking missing parentheses cause syntax error here

5. Given this code, what will Child.new.greet output?

class Parent
  def greet(name = "Guest")
    "Hello, #{name} from Parent"
  end
end

class Child < Parent
  def greet(name = nil)
    if name
      super(name.upcase)
    else
      super()
    end
  end
end

puts Child.new.greet
puts Child.new.greet("alice")

hard

A. Hello, from Parent
Hello, alice from Parent

B. Hello, Guest from Parent
Hello, ALICE from Parent

C. Hello, Guest from Parent
Hello, alice from Parent

D. Error due to wrong arguments in super calls

Solution

1. Step 1: Analyze Child#greet with no argument

   When called without argument, name is nil, so super() calls Parent#greet with no arguments, using default "Guest". When called with "alice", name.upcase is "ALICE" passed to super(name.upcase), so Parent#greet returns "Hello, ALICE from Parent".

2. Final Answer:

   Hello, Guest from Parent Hello, ALICE from Parent -> Option B

3. Quick Check:

   super() calls parent with defaults; super(args) passes modified args [OK]

Hint: Use super() for no args, super(args) to pass specific args [OK]

Common Mistakes:

• Assuming super() passes current args
• Ignoring default parameter in Parent#greet
• Not uppercasing the argument before passing