JuniorTheoryCommon

What does the program print (lines separated by spaces)?

SWIFT

class Person {}
class Flat {
    weak var tenant: Person?
}

var anna: Person? = Person()
let flat = Flat()
flat.tenant = anna
print(flat.tenant == nil)
anna = nil
print(flat.tenant == nil)

false true

Expecting false false: thinking a weak reference keeps the object. It adds nothing to the count, so anna = nil frees the person and tenant becomes nil.
Expecting a crash: mixing up weak with unowned. A weak reference to a freed object is nil, and the program goes on.

What does the program print if tenant is declared without weak?
What happens if you write flat.tenant = Person() instead of using anna?

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JuniorTheoryCommon

What does the program print (lines separated by spaces)?

SWIFT

class Person {}
class Flat {
    weak var tenant: Person?
}

var anna: Person? = Person()
let flat = Flat()
flat.tenant = anna
print(flat.tenant == nil)
anna = nil
print(flat.tenant == nil)

false true

Expecting false false: thinking a weak reference keeps the object. It adds nothing to the count, so anna = nil frees the person and tenant becomes nil.
Expecting a crash: mixing up weak with unowned. A weak reference to a freed object is nil, and the program goes on.

What does the program print if tenant is declared without weak?
What happens if you write flat.tenant = Person() instead of using anna?

Back to questions Open topic in roadmap →Answer it yourself — Quiz