Why extensions add capability without modifying in Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a method to the String type using an extension.

Swift

extension String {
    func shout() -> String {
        return self.[1]uppercased()
    }
}

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

A.

B->

C:

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '->' or ':' instead of '.' to call a method.

In Swift, to call a method on self, you use the dot . operator.

2fill in blank

medium

Complete the code to add a computed property to Int using an extension.

Swift

extension Int {
    var isEven: Bool {
        return self [1] 2 == 0
    }
}

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

A*

B/

C%

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '/' which does division, not remainder.

The modulo operator % gives the remainder. If remainder is 0 when divided by 2, the number is even.

3fill in blank

hard

Fix the error in the extension that adds a method to Double to square the value.

Swift

extension Double {
    func squared() -> Double {
        return self [1] self
    }
}

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' or '-' which add or subtract instead of multiply.

To square a number, multiply it by itself using the * operator.

4fill in blank

hard

Fill both blanks to create an extension that adds a method to Array of Int to sum only positive numbers.

Swift

extension Array where Element == Int {
    func sumPositive() -> Int {
        return self.filter { $0 [1] 0 }.reduce(0, [2])
    }
}

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

A>

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' or '*' in reduce which changes the sum incorrectly.

Filter selects elements greater than 0, then reduce sums them using '+'.

5fill in blank

hard

Fill all three blanks to create an extension that adds a method to Dictionary to get keys with values above a threshold.

Swift

extension Dictionary where Value: Comparable {
    func keysAbove(_ threshold: Value) -> [Key] {
        return self.filter { $0.value [1] threshold }.map { [2].[3] }
    }
}

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

A>

B$0

Ckey

Dkeys

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'keys' property which returns all keys, not filtered ones.

Filter keys where value is greater than threshold, then map to get the keys.