Deinitializers for cleanup in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code using a deinitializer?

Consider this Swift class with a deinitializer. What will be printed when the instance is created and then set to nil?

Swift

class Printer {
    let message: String
    init(message: String) {
        self.message = message
        print("Init: \(message)")
    }
    deinit {
        print("Deinit: \(message)")
    }
}

var p: Printer? = Printer(message: "Hello")
p = nil

A

Init: Hello
Deinit: Hello

B Deinit: Hello

C Init: Hello

D No output

💡 Hint

Think about when the deinitializer runs in Swift.

The initializer prints when the object is created. The deinitializer runs when the object is destroyed, which happens when the variable is set to nil.

❓ Predict Output

intermediate

What happens if a class instance with a deinitializer is never set to nil?

Given this Swift code, what will be the output?

Swift

class Logger {
    deinit {
        print("Logger is being deinitialized")
    }
}

func createLogger() {
    let log = Logger()
    print("Logger created")
}

createLogger()

A No output

B

Logger is being deinitialized
Logger created

C Logger created

D

Logger created
Logger is being deinitialized

💡 Hint

Think about the lifetime of local variables in functions.

The Logger instance is created inside the function and destroyed when the function ends, triggering the deinitializer.

🔧 Debug

advanced

Why does this deinitializer not print anything?

Examine this Swift code. Why does the deinitializer message never appear?

Swift

class Resource {
    deinit {
        print("Resource cleaned up")
    }
}

var r1: Resource? = Resource()
var r2 = r1
r1 = nil
// r2 is still holding the instance

A Because r2 still holds a strong reference, so the instance is not deallocated.

B Because deinit only runs if both variables are nil at the same time.

C Because the deinitializer is not called for optional variables.

D Because the print statement is inside deinit and never executes.

💡 Hint

Think about how Swift manages memory with references.

The instance is kept alive by r2, so deinit does not run until all references are gone.

❓ Predict Output

advanced

What is the output of this Swift code with multiple instances and deinitializers?

Analyze this Swift code and select the correct output sequence.

Swift

class Item {
    let id: Int
    init(id: Int) {
        self.id = id
        print("Init \(id)")
    }
    deinit {
        print("Deinit \(id)")
    }
}

var items: [Item]? = [Item(id: 1), Item(id: 2)]
items?.append(Item(id: 3))
items = nil

A

Init 1
Init 2
Init 3
Deinit 1
Deinit 2
Deinit 3

B

Init 1
Init 2
Init 3

C

Init 1
Init 2
Init 3
Deinit 3
Deinit 2
Deinit 1

D

Init 1
Init 2
Init 3
Deinit 1
Deinit 3
Deinit 2

💡 Hint

Think about the order of initialization and deinitialization of array elements.

All three items are initialized in order. When the array is set to nil, all items are deinitialized in reverse order (last to first).

🧠 Conceptual

expert

Which statement about Swift deinitializers is true?

Choose the correct statement about deinitializers in Swift classes.

A Structs and enums can have deinitializers to clean up resources.

B Deinitializers are called automatically when the last strong reference to an instance is removed.

C You can call a deinitializer explicitly to free resources early.

D A deinitializer can be called multiple times during an object's lifetime.

💡 Hint

Recall how Swift manages memory and object lifecycle.

Deinitializers run once automatically when the last strong reference to a class instance is removed. They cannot be called manually. Structs and enums do not have deinitializers.