Type erasure concept in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of type-erased wrapper usage

What is the output of this Swift code using type erasure with AnySequence?

Swift

struct IntSequence: Sequence {
    func makeIterator() -> some IteratorProtocol {
        return (1...3).makeIterator()
    }
}

let seq: AnySequence<Int> = AnySequence(IntSequence())
for num in seq {
    print(num, terminator: " ")
}

A 1 2 3

B Sequence<Int>

C Compile-time error

D 1 2 3 4

💡 Hint

Think about how AnySequence hides the underlying sequence type but still iterates correctly.

AnySequence erases the concrete type IntSequence but preserves iteration behavior, so it prints 1 2 3.

🧠 Conceptual

intermediate

Purpose of type erasure in Swift

Why do Swift developers use type erasure?

A To enable inheritance between unrelated classes

B To hide concrete types and expose a common interface

C To convert value types into reference types

D To improve runtime performance by avoiding protocols

💡 Hint

Think about how protocols with associated types limit usage.

Type erasure hides the concrete underlying type and exposes a uniform interface, allowing use of protocols with associated types or self requirements.

🔧 Debug

advanced

Fix the error in this type erasure example

What error does this code produce and why? protocol Shape { associatedtype Color func draw() -> Color } struct AnyShape: Shape { private let _draw: () -> C init(_ shape: S) where S.Color == C { _draw = shape.draw } func draw() -> C { _draw() } } struct Circle: Shape { func draw() -> String { "Circle" } } let shape = AnyShape(Circle())

A No error, code compiles successfully

B Error: Cannot convert value of type 'Circle' to expected argument type 'Shape'

C Error: Missing generic argument for 'AnyShape'

D Error: 'Circle' does not conform to 'Shape' because 'Color' is not specified

💡 Hint

Check the associatedtype requirements in the protocol and the struct.

Circle does not specify the associated type 'Color' required by Shape, so it does not conform. This causes a compile error.

📝 Syntax

advanced

Identify the syntax error in this type erasure wrapper

Which option correctly fixes the syntax error in this Swift type erasure code? struct AnyWrapper { private let _value: T init(_ value: T) { _value = value } func getValue() -> T { return _value } } let wrapper = AnyWrapper(5) print(wrapper.getValue()

A Add a closing parenthesis after getValue(): print(wrapper.getValue())

B Change print to println: println(wrapper.getValue())

C Add a semicolon after print: print(wrapper.getValue());

D Replace getValue() with getValue: print(wrapper.getValue)

💡 Hint

Check the parentheses balance in the print statement.

The print statement is missing a closing parenthesis, causing a syntax error. Adding it fixes the code.

🚀 Application

expert

How many elements does this type-erased sequence contain?

Consider this Swift code using type erasure. How many elements will be printed? struct EvenNumbers: Sequence { func makeIterator() -> some IteratorProtocol { (2...10).filter { $0 % 2 == 0 }.makeIterator() } } let numbers = AnySequence(EvenNumbers()) var count = 0 for _ in numbers { count += 1 } print(count)

A 9

B 0

C 5

D 10

💡 Hint

Count even numbers between 2 and 10 inclusive.

Even numbers between 2 and 10 inclusive are 2,4,6,8,10, totaling 5 elements.