Optionals: a value may be absent

A student may not yet have a recorded score. Zero is a real score and should not also mean “missing.” Swift represents possible absence with an optional type, written with a question mark. An Int? contains either an integer or nil; it is not a separate numeric sentinel convention.

What you’ll learn

Represent an absent score with Int? and nil.
Choose an explicit fallback rather than forcing an unwrap.

Optionals: a value may be absent in the example

1
Absent value nil
A student may not yet have a recorded score.
```
Absent value nil
```
→2
Handle absence
An optional must be handled before using its wrapped value as an ordinary Int.
```
Handle absence
```
→3
Present value 80
The initial optional has no value, so the first line displays -1.
```
Present value 80
```

The initial optional has no value, so the first line displays -1. After assignment it contains 80, and the second display uses 80. The negative number is only a visible fallback for this demonstration; the optional itself still distinguishes absence from an actual score.

How optionals: a value may be absent works

An optional must be handled before using its wrapped value as an ordinary Int. ?? supplies a fallback when nil is present. Optional binding lets you work with the value only when available. Force unwrapping with ! asserts a value exists and can trap if that assertion is wrong.

Work through optionals: a value may be absent

Save this complete program as main.swift and run it with the Swift toolchain. No separate input file is needed.

Swift · complete program

var score: Int? = nil
print(score ?? -1)
score = 80
print(score ?? -1)

Expected output

-1
80

Follow the execution

The initial optional has no value, so the first line displays -1. After assignment it contains 80, and the second display uses 80. The negative number is only a visible fallback for this demonstration; the optional itself still distinguishes absence from an actual score.

Try this program in the Swift compiler. Paste the complete source above.

Practice: Optionals: a value may be absent

Your task: Would storing zero instead of nil preserve the distinction between missing and zero marks?

Swift · complete program

var score: Int? = nil
print(score ?? -1)
score = 80
print(score ?? -1)

Worked answer

No. The application could no longer tell a genuine zero from an absent mark without another convention. Int? expresses that distinction directly and requires the program to consider absence.

Represent a missing mark honestly

Do not force unwrap merely to silence a compiler diagnostic. Choose a fallback only if it makes sense for the task; a missing mark might need an “Awaiting result” message rather than arithmetic with -1.

Represent a missing mark honestly

No. The application could no longer tell a genuine zero from an absent mark without another convention. Int? expresses that distinction directly and requires the program to consider absence. Do not force unwrap merely to silence a compiler diagnostic.

Further reading: official Swift language guide.

Reaching the recap and completing the quizzes are separate milestones.

Next lesson: Optional binding and chaining →

Optionals: a value may be absent