CompactMap for optional unwrapping in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does compactMap do in Swift?

compactMap takes a collection and transforms its elements, removing any nil values from the result. It unwraps optionals safely and returns an array of non-optional values.

beginner

How is compactMap different from map when dealing with optionals?

map transforms elements but keeps optionals in the result, while compactMap unwraps optionals and removes nil values, returning only non-optional results.

beginner

Example: What is the result of ["1", "2", "three", "4"].compactMap { Int($0) }?

The result is [1, 2, 4]. The string "three" cannot be converted to an integer, so it becomes nil and is removed.

intermediate

Why use compactMap instead of a loop with manual unwrapping?

compactMap is concise, safe, and expressive. It avoids errors from forced unwrapping and makes code easier to read by handling optionals automatically.

intermediate

Can compactMap be used to filter and transform elements at the same time?

Yes! compactMap lets you transform elements and automatically removes any that become nil, effectively filtering and mapping in one step.

What does compactMap return when applied to an array with some nil values?

A A single optional value

B An array including <code>nil</code> values

C An array without the <code>nil</code> values, unwrapped

D A dictionary of values

compactMap removes nil values and unwraps optionals, returning only non-optional elements.

Which method keeps nil values in the result when transforming an array of optionals?

A compactMap

B map

C filter

D reduce

map transforms elements but keeps nil values as optionals in the result.

What is the output of ["10", "abc", "30"].compactMap { Int($0) }?

A [10, 30]

B ["10", "abc", "30"]

C [10, nil, 30]

D nil

Only "10" and "30" convert to integers; "abc" becomes nil and is removed.

Why is compactMap safer than forced unwrapping when dealing with optionals?

A It automatically removes <code>nil</code> values without crashing

B It forces unwraps all values

C It converts all values to strings

D It ignores all optionals

compactMap safely unwraps optionals and skips nil values, preventing runtime crashes.

Can compactMap be used to both filter and transform an array?

A No, it neither filters nor transforms

B No, it only filters

C No, it only transforms

D Yes, it filters out <code>nil</code> and transforms elements

compactMap transforms elements and removes nil results, combining filtering and mapping.

Explain how compactMap helps in unwrapping optionals in Swift collections.

Think about how it handles nil and non-nil values during transformation.

Describe a real-life scenario where using compactMap is better than using map with forced unwrapping.

Consider converting user input strings to numbers.