Weak self and unowned self patterns in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of using weak self in Swift closures?

Using weak self prevents strong reference cycles by creating a weak reference to self inside a closure. This means the closure does not keep self alive, avoiding memory leaks.

intermediate

How does unowned self differ from weak self in Swift?

unowned self is a non-optional reference that assumes self will always exist when the closure runs. Unlike weak self, it does not become nil. Use it when self is guaranteed to outlive the closure.

beginner

What happens if you access self inside a closure without weak or unowned?

Accessing self strongly inside a closure creates a strong reference cycle if self also holds the closure. This causes a memory leak because neither can be released.

intermediate

When should you use weak self instead of unowned self?

Use weak self when self might become nil before the closure finishes. This makes self optional inside the closure, so you must safely unwrap it.

beginner

Explain a real-life analogy for weak and unowned references.

Imagine self is a person and the closure is a friend holding a photo. weak means the friend holds a photo that can fade (become nil) if the person leaves. unowned means the friend holds a photo that never fades because the person is always around.

What does weak self create inside a closure?

A A weak, optional reference to self

B A strong reference to self

C A non-optional unowned reference to self

D A copy of self

weak self creates a weak, optional reference to self to avoid strong reference cycles.

When should you use unowned self in a closure?

A When you want to copy self

B When self might be nil during closure execution

C When self is guaranteed to exist during closure execution

D When you want to create a strong reference cycle

unowned self is used when self will definitely exist while the closure runs.

What risk do you take when using unowned self incorrectly?

A Crash due to accessing nil reference

B Memory leak

C Slower performance

D No risk at all

If self is nil but accessed as unowned, the app will crash.

Which keyword makes self optional inside a closure?

A strong

B unowned

C let

D weak

weak makes self optional because it can become nil.

Why do we avoid strong references to self inside closures?

A To improve code readability

B To prevent strong reference cycles and memory leaks

C To make code run faster

D To copy self

Strong references inside closures can cause memory leaks by creating cycles.

Explain the difference between weak self and unowned self in Swift closures.

Think about whether self can be nil or not during closure execution.

Describe a situation where using weak self is necessary to avoid a memory leak.

Consider when self and closure keep each other alive.