Array creation and type inference in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is type inference in Swift when creating an array?

Type inference means Swift automatically figures out the type of the array based on the values you put inside it, so you don't have to write the type explicitly.

beginner

How do you create an empty array of integers in Swift?

You can create it by writing: var numbers: [Int] = [] or var numbers = [Int]().

beginner

What happens if you write <code>let fruits = ["Apple", "Banana", "Cherry"]</code> in Swift?

Swift infers that fruits is an array of strings: [String].

intermediate

Can Swift infer the type of an array if it contains mixed types like [1, "two", 3]?

No, Swift requires all elements in an array to be of the same type. Mixed types cause a compile error.

beginner

How do you create an array with repeated values in Swift?

Use Array(repeating: value, count: number). For example, Array(repeating: 0, count: 3) creates [0, 0, 0].

What type does Swift infer for let numbers = [1, 2, 3]?

A [Int]

B [Double]

C [String]

D [Any]

Swift sees all values are integers, so it infers the array type as [Int].

Which of these is a valid way to create an empty array of strings in Swift?

A var names = [String]

B var names = []

C var names = [1, 2, 3]

D var names: [String] = []

You must specify the type when creating an empty array, like var names: [String] = [].

What happens if you try to create let mixed = [1, "two", 3] in Swift?

A Swift infers [Any]

B Swift infers [String]

C Compile error due to mixed types

D Swift infers [Int]

Swift arrays must have elements of the same type; mixed types cause a compile error.

How do you create an array with five zeros in Swift?

A [0, 0, 0, 0, 0]

B Array(repeating: 0, count: 5)

C Array(0, 5)

D repeat(0, 5)

Use Array(repeating: 0, count: 5) to create an array with five zeros.

If you write var items = ["pen", "pencil"], what is the type of items?

A [String]

B [Character]

C [Any]

D [Int]

Swift infers the type as [String] because all elements are strings.

Explain how Swift uses type inference when you create an array with values.

Think about how Swift guesses the type based on what you put inside the array.

Describe two ways to create an empty array in Swift and why you might need to specify the type.

Remember empty arrays have no values, so Swift can't guess the type automatically.