Typealias for custom naming in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of code using typealias with struct

What is the output of this Swift code using typealias for a custom name?

Swift

struct Point {
    var x: Int
    var y: Int
}
typealias Coordinate = Point

let p: Coordinate = Coordinate(x: 3, y: 4)
print("x: \(p.x), y: \(p.y)")

A x: 3, y: 4

B x: 4, y: 3

C Compile error: Cannot assign to typealias

D Runtime error: Unexpected nil value

💡 Hint

Remember that typealias just creates a new name for an existing type.

The typealias 'Coordinate' is just another name for 'Point'. So creating a Coordinate instance is the same as creating a Point instance. The values x=3 and y=4 are printed as expected.

❓ Predict Output

intermediate

Output of typealias with function type

What will this Swift code print when using typealias for a function type?

Swift

typealias Operation = (Int, Int) -> Int

func add(_ a: Int, _ b: Int) -> Int {
    return a + b
}

let op: Operation = add
print(op(5, 7))

A Compile error: Cannot assign function to typealias

B 12

C 57

D Runtime error: Function not found

💡 Hint

A typealias for a function type can be used to declare variables holding functions.

The typealias 'Operation' defines a function type taking two Ints and returning an Int. The function 'add' matches this type. Calling op(5,7) returns 12.

❓ Predict Output

advanced

Output of nested typealias usage

What is the output of this Swift code using nested typealias inside a struct?

Swift

struct Container {
    typealias Item = String
    var items: [Item]
}

let c = Container(items: ["apple", "banana"])
print(c.items[1])

A Runtime error: Index out of range

B apple

C banana

D Compile error: Cannot use typealias inside struct

💡 Hint

Typealias inside a struct can be used as a shorthand for types used in the struct.

The typealias 'Item' is String. The array contains two strings. Accessing index 1 returns 'banana'.

❓ Predict Output

advanced

Output of typealias with tuple type

What will this Swift code print when using typealias for a tuple type?

Swift

typealias NameAge = (name: String, age: Int)

let person: NameAge = (name: "John", age: 30)
print("\(person.name) is \(person.age) years old")

A Runtime error: Missing tuple element

B (John, 30)

C Compile error: Cannot use tuple with typealias

D John is 30 years old

💡 Hint

Typealias can be used to name tuple types for easier reuse.

The typealias 'NameAge' names a tuple type with named elements. Printing person.name and person.age works as expected.

❓ Predict Output

expert

Output of typealias with generic type aliasing

What is the output of this Swift code using a generic typealias?

Swift

typealias Pair<T> = (first: T, second: T)

let numbers: Pair<Int> = (first: 10, second: 20)
let words: Pair<String> = (first: "hello", second: "world")
print(numbers.first + numbers.second)
print(words.first + " " + words.second)

A

30
hello world

B

1020
hello world

C Compile error: Generic typealias not supported

D Runtime error: Cannot add Int and String

💡 Hint

Generic typealias can create reusable tuple types with different element types.

The generic typealias 'Pair' defines a tuple with two elements of type T. For Int, adding 10 + 20 gives 30. For String, concatenation with space prints 'hello world'.