why is self nil in weak self

In Swift, weak references are used to avoid creating strong reference cycles, which can lead to memory leaks. A weak reference does not increase the reference count of the object it points to. This means that when the object is deallocated, the weak reference automatically becomes nil. This is why self can be nil when using weak self in a closure or other context.

Here are some key points from the WWDC sessions that explain this behavior:

1. Weak References and Deinitialization:

   • Weak references are always optional types and become nil after their destinations are deinitialized. This allows the weak references to be lazily set to nil after the object they reference is deallocated. (Analyze heap memory)

2. Avoiding Strong Reference Cycles:

   • Weak references are used to avoid increasing the reference count on an object, which helps in breaking strong reference cycles. When the object being referenced is deallocated, the weak reference becomes nil. (A Swift Tour: Explore Swift’s features and design)

3. Performance Considerations:

   • Weak references come with some overhead because Swift allocates a weak reference storage for the destination object the first time it's weakly referenced. This storage allows the weak references to be set to nil when the object is deallocated. (Analyze heap memory)

4. Comparison with Unowned References:

   • Unlike weak references, unowned references directly hold their destinations and do not become nil. However, they can lead to crashes if accessed after the destination object is deallocated. (Analyze heap memory)

Relevant Sessions

• Analyze heap memory
• A Swift Tour: Explore Swift’s features and design

These sessions provide a detailed explanation of how weak references work in Swift and why they become nil when the referenced object is deallocated.