Nil coalescing operator deep usage in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Nil Coalescing with Optional Chaining

What is the output of this Swift code snippet?

Swift

struct User {
    var name: String?
}

let user: User? = User(name: nil)
let displayName = user?.name ?? "Guest"
print(displayName)

A nil

B "Guest"

C "Optional(nil)"

D Compilation error

💡 Hint

Remember that optional chaining returns an optional, and nil coalescing provides a default value.

The optional chaining user?.name returns nil because name is nil. The nil coalescing operator then provides "Guest" as the default value.

❓ Predict Output

intermediate

Nested Nil Coalescing Operators

What will be printed by this Swift code?

Swift

let a: Int? = nil
let b: Int? = 5
let c: Int? = nil

let result = a ?? b ?? c ?? 10
print(result)

A 5

B nil

C 10

D Compilation error

💡 Hint

The nil coalescing operator evaluates from left to right until it finds a non-nil value.

a is nil, so it checks b which is 5 (non-nil), so result is 5.

🔧 Debug

advanced

Unexpected Behavior with Nil Coalescing and Function Calls

Consider this Swift code. What is the output and why?

Swift

func getValue() -> Int? {
    print("getValue called")
    return nil
}

let x: Int? = nil
let y = x ?? getValue() ?? 42
print(y)

A getValue called\nnil

B 42

C getValue called\n42

D Compilation error

💡 Hint

Check when the function getValue() is called in the nil coalescing chain.

Since x is nil, getValue() is called and prints "getValue called". It returns nil, so the final value is 42.

📝 Syntax

advanced

Correct Usage of Nil Coalescing with Optional Binding

Which option correctly uses nil coalescing to assign a non-optional Int from an optional Int?

A let value = optionalInt ?? 0

B let value = optionalInt ? 0

C let value = optionalInt || 0

D let value = optionalInt ?: 0

💡 Hint

The nil coalescing operator in Swift is ??

Option A uses the correct nil coalescing operator ?? to provide a default value.

🚀 Application

expert

Complex Nil Coalescing in Dictionary Lookup

Given this Swift code, what is the value of finalValue after execution?

Swift

let dict: [String: Int?] = ["a": 1, "b": nil]

let finalValue = dict["b"] ?? (10 as Int?)
print(finalValue ?? -1)

A -1

B 10

C 1

D nil

💡 Hint

Remember the dictionary value is an optional Int optional, so dict["b"] returns Int??

dict["b"] returns an optional Int? which is .some(nil). The nil coalescing operator unwraps only the outer optional, so finalValue is nil.