Nil coalescing operator deep usage 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. It unwraps the optional if it has a value, otherwise returns the default value.

intermediate

How can you chain multiple nil coalescing operators?

You can chain them like: optional1 ?? optional2 ?? defaultValue. Swift evaluates from left to right and returns the first non-nil value.

intermediate

Can the right side of the nil coalescing operator be another optional?

Yes, but the result will be an optional if the right side is optional. To get a non-optional result, the right side should be a non-optional value.

beginner

Explain how nil coalescing operator helps avoid nested if-let statements.

Instead of multiple nested if-let to unwrap optionals, you can use ?? to provide defaults and simplify code, making it cleaner and easier to read.

advanced

What happens if you use nil coalescing operator with a function call on the right side?

The function is only called if the left optional is nil. This is useful for lazy evaluation or expensive default value calculations.

What will this Swift code print? <br> let a: Int? = nil <br> let b = a ?? 5

A 5

B nil

C 0

D Compilation error

Since 'a' is nil, the nil coalescing operator returns the default value 5.

Which of these is a valid use of chaining nil coalescing operators?

A let x = a ?? b ?? 10

B let x = a ?? ?? 10

C let x = ?? a ?? 10

D let x = a ?? b ??

Chaining like 'a ?? b ?? 10' is valid and returns the first non-nil value.

If 'a' is Int? and 'b' is Int?, what is the type of 'a ?? b'?

A Compilation error

B Int

C Optional<Optional<Int>>

D Int?

If the right side is optional, the result remains optional.

When is the right side expression of '??' evaluated?

A Only if the left side is non-nil

B Only if the left side is nil

C Never

D Always

The right side is evaluated only if the left side is nil, enabling lazy evaluation.

Which statement about nil coalescing operator is false?

A It unwraps optionals or returns a default value

B It can chain multiple optionals

C It always returns a non-optional value

D It evaluates the right side lazily

It does not always return a non-optional; if the right side is optional, the result can be optional.

Explain how the nil coalescing operator (??) works in Swift and give an example of chaining it with multiple optionals.

Think about how it picks the first non-nil value.

Describe a scenario where using the nil coalescing operator with a function call on the right side is beneficial.

Consider when the default value is expensive to compute.