Composing property wrappers in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a property wrapper named Capitalized that capitalizes a string.

Swift

@propertyWrapper struct Capitalized {
    private var value: String = ""
    var wrappedValue: String {
        get { value }
        set { value = newValue.capitalized }
    }
    init(wrappedValue: String) {
        self.value = wrappedValue.capitalized
    }
}

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A.capitalized

B.uppercased()

C.lowercased()

D.trimmingCharacters(in: .whitespaces)

Attempts:

3 left

💡 Hint

Common Mistakes

Using .uppercased() which makes all letters uppercase instead of capitalizing each word.

Using .lowercased() which makes all letters lowercase.

Forgetting to capitalize the new value in the setter.

The wrappedValue setter should capitalize the new string value, so .capitalized is the correct method.

2fill in blank

medium

Complete the code to apply two property wrappers Trimmed and Capitalized to a string property name.

Swift

struct User {
    @[1] @Capitalized var name: String
}

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ATrimmed

BLazy

CPublished

DState

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated wrappers like @Lazy or @State which do not trim strings.

Applying wrappers in the wrong order.

The Trimmed wrapper should be applied before Capitalized to trim whitespace before capitalizing.

3fill in blank

hard

Fix the error in the composed property wrappers by completing the code to delegate projectedValue correctly.

Swift

@propertyWrapper struct Trimmed {
    private var value: String = ""
    var wrappedValue: String {
        get { value }
        set { value = newValue.trimmingCharacters(in: .whitespaces) }
    }
    var projectedValue: String { $[1] }
    init(wrappedValue: String) {
        self.value = wrappedValue.trimmingCharacters(in: .whitespaces)
    }
}

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Avalue

BprojectedValue

Cself

DwrappedValue

Attempts:

3 left

💡 Hint

Common Mistakes

Returning value directly which bypasses the wrapper logic.

Returning projectedValue recursively causing infinite loop.

The projectedValue should delegate to wrappedValue to expose the trimmed string.

4fill in blank

hard

Fill both blanks to create a composed property wrapper TrimmedCapitalized that applies Trimmed and Capitalized wrappers.

Swift

@propertyWrapper struct TrimmedCapitalized {
    @Trimmed var trimmed: String
    @Capitalized var capitalized: String

    var wrappedValue: String {
        get { [1] }
        set {
            [2] = newValue
            capitalized = newValue
        }
    }

    init(wrappedValue: String) {
        self.trimmed = wrappedValue
        self.capitalized = wrappedValue
    }
}

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Atrimmed

Bcapitalized

Cself.trimmed

Dself.capitalized

Attempts:

3 left

💡 Hint

Common Mistakes

Using just trimmed without self. which can cause ambiguity.

Setting capitalized before trimmed causing wrong order.

The getter and setter should use self.trimmed to get and set the trimmed value before capitalizing.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that creates a dictionary with keys as uppercased trimmed words and values as their capitalized versions.

Swift

let words = ["  hello", "world  ", " swift"]
let transformed = [
    [1]: [2] for word in words
    if word[3] " "
]

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Aword.trimmingCharacters(in: .whitespaces).uppercased()

Bword.capitalized

C.contains

D.hasPrefix

Attempts:

3 left

💡 Hint

Common Mistakes

Using .hasPrefix instead of .contains for filtering.

Not trimming whitespace before uppercasing the key.

Using the raw word instead of capitalized for the value.

The key is the trimmed and uppercased word, the value is the capitalized word, and the filter checks if the word contains a space.