Why optionals are Swift's core safety feature - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an optional integer variable.

Swift

var number: Int[1]

Drag options to blanks, or click blank then click option'

A?

B!

C=

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!' instead of '?' to declare an optional.

Forgetting to add any symbol after the type.

In Swift, adding a ? after a type declares it as optional, meaning it can hold a value or be nil.

2fill in blank

medium

Complete the code to safely unwrap an optional using if-let.

Swift

if let safeNumber = optionalNumber[1] { print(safeNumber) }

Drag options to blanks, or click blank then click option'

A!

B?

C=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '=' in if-let.

Using '!' or '?' in this context.

The if let syntax uses = to assign the unwrapped value if it exists.

3fill in blank

hard

Fix the error in force unwrapping an optional.

Swift

let forcedValue = optionalValue[1]

Drag options to blanks, or click blank then click option'

A?

B:

C=

D!

Attempts:

3 left

💡 Hint

Common Mistakes

Using '?' instead of '!' for force unwrapping.

Using '=' or ':' which are invalid here.

Force unwrapping uses ! to get the value inside an optional, but it can crash if nil.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension filtering non-nil values.

Swift

let filtered = dictionary.compactMapValues { $0[1] } .filter { $0[2] nil }

Drag options to blanks, or click blank then click option'

A!

B==

C!=

D?

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!' in optional chaining which can cause crashes.

Using '==' instead of '!=' to filter nil.

Use ? to safely unwrap in compactMapValues and != to filter out nil values.

5fill in blank

hard

Fill all three blanks to unwrap an optional with guard and provide a default value.

Swift

guard let value = optionalValue[1] else { return [2] } let finalValue = value[3]

Drag options to blanks, or click blank then click option'

A?

B0

D!

Attempts:

3 left

💡 Hint

Common Mistakes

Not using guard let syntax correctly.

Returning nil instead of a default value.

Forgetting to unwrap after guard.

Use ? for optional chaining, 0 as default return, and ! to force unwrap after guard.