Calling super for parent behavior in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code using super?

Consider the following Swift classes. What will be printed when Child().greet() is called?

Swift

class Parent {
    func greet() {
        print("Hello from Parent")
    }
}

class Child: Parent {
    override func greet() {
        super.greet()
        print("Hello from Child")
    }
}

Child().greet()

A Hello from Child\nHello from Parent

B Hello from Child

C Hello from Parent\nHello from Child

D Hello from Parent

💡 Hint

Remember that super.greet() calls the parent class method first.

The Child class overrides greet() and calls super.greet() first, which prints "Hello from Parent". Then it prints "Hello from Child".

🧠 Conceptual

intermediate

Why use super in Swift class methods?

Which of the following best explains why you would call super.method() inside an overridden method?

A To prevent the parent class method from running.

B To call the parent class's implementation and add extra behavior in the child class.

C To call a method from a sibling class.

D To create a new method unrelated to the parent.

💡 Hint

Think about how inheritance works and extending behavior.

Calling super.method() lets the child class reuse the parent class's code and then add or change behavior.

🔧 Debug

advanced

What error occurs when calling super in a Swift initializer incorrectly?

Examine this Swift code snippet. What error will it produce?

Swift

class Parent {
    init() {
        print("Parent init")
    }
}

class Child: Parent {
    override init() {
        print(self)
        super.init()
    }
}

A Error: Cannot override initializer in subclass

B No error, prints 'Child init' then 'Parent init'

C Error: Missing required initializer

D Error: 'super.init()' must be called before accessing self or properties

💡 Hint

Swift requires calling super.init() before using self in initializers.

In Swift, you must call super.init() before accessing self or its properties in an initializer. Printing before calling super.init() accesses self, causing an error.

📝 Syntax

advanced

Which option correctly calls the parent method in Swift?

Which of the following is the correct way to call a parent class method named display() inside an overridden method?

A super.display()

B Parent.display()

C self.super.display()

D super->display()

💡 Hint

Remember the Swift syntax for calling parent methods.

In Swift, super.methodName() calls the parent class's method. Other options are invalid syntax.

🚀 Application

expert

What is the final value of count after calling increment() twice?

Given these Swift classes, what is the value of count after Child().increment() is called twice?

Swift

class Parent {
    var count = 0
    func increment() {
        count += 1
    }
}

class Child: Parent {
    override func increment() {
        super.increment()
        count += 2
    }
}

let obj = Child()
obj.increment()
obj.increment()
print(obj.count)

A 6

B 4

C 2

D 8

💡 Hint

Each call adds 1 from super.increment() and 2 more in Child.increment().

Each increment() call adds 3 to count (1 from parent, 2 from child). Two calls add 6 total.

Practice

1. What does calling super.methodName() inside an overridden method in Swift do?

easy

A. It runs the parent class's version of the method.

B. It creates a new method unrelated to the parent.

C. It deletes the parent class's method.

D. It calls a method from a sibling class.

Solution

1. Step 1: Understand method overriding

   When a subclass overrides a method, it replaces the parent's method behavior.

2. Step 2: Role of super

   Calling super.methodName() runs the original method from the parent class, preserving its behavior.

3. Final Answer:

   It runs the parent class's version of the method. -> Option A

4. Quick Check:

   Calling super runs parent method [OK]

Hint: Remember: super calls parent method inside override [OK]

Common Mistakes:

• Thinking super creates a new method
• Believing super deletes parent methods
• Confusing super with sibling class calls

2. Which of the following is the correct syntax to call a parent class's method named display() inside an overridden method in Swift?

easy

A. super.display()

B. parent.display()

C. self.super.display()

D. super::display()

Solution

1. Step 1: Identify Swift syntax for super calls

   Swift uses the keyword super followed by dot and method name to call parent methods.

2. Step 2: Check each option

   Only super.display() matches Swift syntax. Others are invalid or from other languages.

3. Final Answer:

   super.display() -> Option A

4. Quick Check:

   super.methodName() is correct syntax [OK]

Hint: Use super.methodName() to call parent method [OK]

Common Mistakes:

• Using parent instead of super
• Adding self before super
• Using :: like in C++

3. Consider this Swift code:

class Parent {
    func greet() {
        print("Hello from Parent")
    }
}

class Child: Parent {
    override func greet() {
        print("Child starts")
        super.greet()
        print("Child ends")
    }
}

let c = Child()
c.greet()

What is the output when c.greet() is called?

medium

A. Child starts\nChild ends\nHello from Parent

B. Child starts\nHello from Parent\nChild ends

C. Hello from Parent

D. Hello from Parent\nChild starts\nChild ends

Solution

1. Step 1: Trace the overridden method

   The greet() method in Child prints "Child starts", then calls super.greet() which prints "Hello from Parent", then prints "Child ends".

2. Step 2: Combine outputs in order

   Output lines are: "Child starts", "Hello from Parent", "Child ends" in that order.

3. Final Answer:

   Child starts Hello from Parent Child ends -> Option B

4. Quick Check:

   super call runs parent method in middle [OK]

Hint: Follow print order: before, super call, after [OK]

Common Mistakes:

• Ignoring order of prints
• Assuming super call is last
• Mixing output lines

4. This Swift code tries to override a method but causes an error:

class Parent {
    func show() {
        print("Parent show")
    }
}

class Child: Parent {
    override func show() {
        print("Child show")
        show()  // Line X
    }
}

What is the problem and how to fix it?

medium

A. Missing super keyword before override.

B. Method name mismatch; rename show() in Child.

C. Cannot override non-virtual method; remove override keyword.

D. Line X causes infinite recursion; fix by calling super.show() instead.

Solution

1. Step 1: Identify recursion cause

   Inside Child.show(), calling show() calls itself again, causing infinite recursion.

2. Step 2: Correct call to parent method

   Use super.show() to call the parent class's method and avoid recursion.

3. Final Answer:

   Line X causes infinite recursion; fix by calling super.show() instead. -> Option D

4. Quick Check:

   Call super.method() to avoid recursion [OK]

Hint: Use super.method() inside override to avoid recursion [OK]

Common Mistakes:

• Calling method without super inside override
• Removing override keyword incorrectly
• Changing method name unnecessarily

5. You have a class hierarchy where Grandparent has a method log(), Parent overrides it and calls super.log(), and Child overrides it too. You want Child.log() to add its own message, then call Parent.log(), which calls Grandparent.log(). How should you write Child.log() to achieve this?

hard

A. override func log() { print("Child log") }

B. override func log() { super.log() ; print("Child log") }

C. override func log() { print("Child log") ; super.log() }

D. override func log() { Parent.log() ; print("Child log") }

Solution

1. Step 1: Understand call chain

   Calling super.log() in Child calls Parent.log(), which calls Grandparent.log().

2. Step 2: Add Child's message before calling super

   To add Child's message first, print it, then call super.log().

3. Final Answer:

   override func log() { print("Child log") ; super.log() } -> Option C

4. Quick Check:

   Print then super.log() for correct order [OK]

Hint: Print first, then call super to keep parent behavior [OK]

Common Mistakes:

• Calling super before print changes order
• Not calling super loses parent logs
• Trying to call Parent.log() directly (not allowed)