Type erasure concept in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a protocol with an associated type.

Swift

protocol Container {
    associatedtype Item
    func add(_ item: [1])
}

Drag options to blanks, or click blank then click option'

AInt

BItem

CAny

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using a concrete type like Int or String instead of the associatedtype.

Using Any which loses type information.

The protocol uses an associated type named Item, so the add function parameter must be of type Item.

2fill in blank

medium

Complete the code to define a type-erased wrapper class for the Container protocol.

Swift

class AnyContainer<T>: Container {
    private let _add: (T) -> Void

    init<C: Container>(_ container: C) where C.Item == T {
        _add = container.add
    }

    func add(_ item: [1]) {
        _add(item)
    }
}

Drag options to blanks, or click blank then click option'

AT

BItem

CContainer

DAny

Attempts:

3 left

💡 Hint

Common Mistakes

Using Any loses type safety.

Using Container or Item as parameter types is incorrect here.

The add function parameter must be of the generic type T to match the Container protocol's associated type.

3fill in blank

hard

Fix the error in the type-erased wrapper initializer to correctly capture the add method.

Swift

init<C: Container>(_ container: C) where C.Item == T {
    _add = container.[1]
}

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Aadd(item:)

Badd

Cadd()

Dadd(_:)

Attempts:

3 left

💡 Hint

Common Mistakes

Using add() calls the method instead of referencing it.

Using add without parameter label causes errors.

To assign the method as a closure, use the method reference with parameter label and colon: add(_:).

4fill in blank

hard

Fill both blanks to complete a type-erased container that stores elements and erases type.

Swift

class AnyContainer<T>: Container {
    private var items: [T] = []
    private let _add: (T) -> Void

    init<C: Container>(_ container: C) where C.Item == T {
        _add = container.[1]
    }

    func add(_ item: [2]) {
        items.append(item)
        _add(item)
    }
}

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Aadd(_:)

Badd()

CT

DAny

Attempts:

3 left

💡 Hint

Common Mistakes

Using add() calls the method instead of referencing it.

Using Any as parameter type loses type safety.

The method reference must be add(_:), and the add function parameter type is the generic T.

5fill in blank

hard

Fill all three blanks to create a type-erased container that forwards add calls and stores items.

Swift

class AnyContainer<T>: Container {
    private var items: [[1]] = []
    private let _add: (T) -> Void

    init<C: Container>(_ container: C) where C.Item == [2] {
        _add = container.[3]
    }

    func add(_ item: T) {
        items.append(item)
        _add(item)
    }
}

Drag options to blanks, or click blank then click option'

AT

BItem

Cadd(_:)

DAny

Attempts:

3 left

💡 Hint

Common Mistakes

Using Item instead of T in the array or constraint.

Using Any loses type safety.

Using add() calls the method instead of referencing it.

The items array stores elements of type T, the initializer constraint uses C.Item == T, and the method reference is add(_:).