Nil coalescing operator (??) in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nil coalescing with optional Int

What is the output of this Swift code snippet?

Swift

let a: Int? = nil
let b = a ?? 10
print(b)

A Compilation error

B nil

C 0

D 10

💡 Hint

Remember, the nil coalescing operator returns the left value if it is not nil, otherwise the right value.

Since 'a' is nil, the expression 'a ?? 10' returns 10. So, the printed output is 10.

❓ Predict Output

intermediate

Nil coalescing with non-nil optional

What will be printed by this Swift code?

Swift

let name: String? = "Alice"
let displayName = name ?? "Guest"
print(displayName)

A Alice

B nil

C Guest

D Compilation error

💡 Hint

If the optional has a value, the nil coalescing operator returns that value.

The optional 'name' contains "Alice", so 'name ?? "Guest"' evaluates to "Alice".

❓ Predict Output

advanced

Chained nil coalescing operator output

What is the output of this Swift code?

Swift

let x: Int? = nil
let y: Int? = 5
let z = x ?? y ?? 10
print(z)

A Compilation error

B nil

C 5

D 10

💡 Hint

The nil coalescing operator can be chained to check multiple optionals.

Since 'x' is nil, it checks 'y' which is 5, so 'z' becomes 5.

❓ Predict Output

advanced

Nil coalescing with different types

What error or output occurs when running this Swift code?

Swift

let a: Int? = nil
let b = a ?? "default"
print(b)

A nil

B Compilation error

C default

D Optional("")

💡 Hint

The nil coalescing operator requires both sides to have the same type.

The left side is Int? and the right side is String, so the compiler reports a type mismatch error.

🧠 Conceptual

expert

Behavior of nil coalescing with function returning optional

Consider the following Swift code. What is the value of 'result' after execution?

Swift

func fetchValue() -> Int? {
    return nil
}

let result = fetchValue() ?? 42

A 42

B nil

C Compilation error

D Optional(42)

💡 Hint

The function returns nil, so the nil coalescing operator uses the default value.

Since fetchValue() returns nil, 'result' is assigned the default value 42.