Capturing values from context in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to capture the value of 'number' inside the closure.

Swift

let number = 10
let closure = { print([1]) }
closure()

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Anumber

Bself.number

Cnum

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name that is not defined in the current scope.

Trying to use 'self.number' when 'number' is not a property.

The closure captures the variable 'number' from its surrounding context, so using 'number' inside the closure prints its value.

2fill in blank

medium

Complete the code to capture the value of 'count' as a constant inside the closure.

Swift

var count = 5
let closure = { [[1]] in
    print(count)
}
count = 10
closure()

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Avar count

Bself.count

Clet count

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Writing 'var count' or 'let count' inside the capture list, which is invalid syntax.

Not using a capture list and expecting the closure to capture the value at definition time.

Using '[count]' in the capture list captures the current value of 'count' as a constant inside the closure.

3fill in blank

hard

Fix the error in the closure to capture 'self' weakly to avoid retain cycles.

Swift

class MyClass {
    var value = 42
    func doWork() {
        let closure = { [[1] self] in
            print(self.value)
        }
        closure()
    }
}

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Avar

Bweak

Cstrong

Dunowned

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'strong' or 'var' in the capture list, which are invalid.

Not capturing 'self' weakly, causing memory leaks.

Using '[weak self]' captures 'self' weakly inside the closure, preventing retain cycles.

4fill in blank

hard

Fill both blanks to capture 'value' strongly and 'count' weakly inside the closure.

Swift

var value = 100
var count = 20
let closure = { [[1] value, [2] count] in
    print(value, count ?? 0)
}
closure()

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Avalue

Bweak

Cunowned

Dstrong

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to write 'strong value' which is invalid syntax.

Not using 'weak' before 'count' to capture it weakly.

'value' is captured strongly by default, so just listing 'value' captures it strongly. 'count' is captured weakly using 'weak count'.

5fill in blank

hard

Fill all three blanks to capture 'name' unowned, 'age' weakly, and 'score' strongly inside the closure.

Swift

var name = "Alice"
var age: Int? = 30
var score = 95
let closure = { [[1] name, [2] age, [3] score] in
    print(name, age ?? 0, score)
}
closure()

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

Aunowned

Bweak

Cscore

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of capture modifiers and variable names.

Trying to write 'strong score' which is invalid syntax.

'name' is captured unowned, so 'unowned name'. 'age' is captured weakly, so 'weak age'. 'score' is captured strongly by default, so just 'score'.