Nil coalescing operator (??) in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the nil coalescing operator (??) do in Swift?

It provides a default value when an optional is nil. If the optional has a value, it unwraps and returns it; otherwise, it returns the default value.

beginner

How would you use the nil coalescing operator to assign a default name if a variable 'username' is nil?

You write: let name = username ?? "Guest". This means if 'username' is nil, 'name' will be "Guest".

beginner

True or False: The nil coalescing operator (??) can only be used with optional values.

True. It is designed to work with optionals to provide a fallback value when the optional is nil.

beginner

What is the result of this Swift code? <br><pre>let a: Int? = nil<br>let b = a ?? 10</pre>

The value of 'b' will be 10 because 'a' is nil, so the nil coalescing operator returns the default value 10.

intermediate

Explain why nil coalescing operator (??) is useful in real-life programming.

It helps avoid crashes by safely unwrapping optionals and providing a fallback value, making code simpler and safer when dealing with missing data.

What does the nil coalescing operator (??) return if the optional on the left is not nil?

A The unwrapped value of the optional

B The default value on the right

C nil

D An error

If the optional has a value, the operator returns that value instead of the default.

Which of these is a correct use of the nil coalescing operator?

A let result = optionalValue ?? 5

B let result = 5 ?? optionalValue

C let result = optionalValue ? 5

D let result = optionalValue || 5

The operator is used as 'optional ?? defaultValue'.

If you have 'let x: String? = nil', what is the value of 'let y = x ?? "Hello"'?

A "Hello"

B nil

C x

D An error

Since x is nil, y gets the default string "Hello".

Can the nil coalescing operator be chained like 'a ?? b ?? c'?

A Yes, it returns the first non-nil value

B No, it causes a syntax error

C Only if all are integers

D Only if all are strings

You can chain it to check multiple optionals and get the first non-nil value.

What type must the right side of the nil coalescing operator have?

A The same type as the unwrapped optional

B Any type

C Only optional types

D Only String type

The default value must match the type of the optional's unwrapped value.

Describe how the nil coalescing operator (??) works in Swift and give a simple example.

Think about how to handle missing values safely.

Why is using the nil coalescing operator better than force unwrapping optionals?

Consider what happens if the optional is nil.