Swift Advanced Concepts - Programming

It is a design approach favoring composition of protocols with default implementations in extensions over deep class inheritance. Types adopt the behaviors they need, and protocol extensions supply shared logic, giving flexibility and reuse while keeping the benefits of value types.

Automatic Reference Counting tracks how many strong references point to each class instance and frees it when the count reaches zero. Because two objects referencing each other strongly never reach zero, you break such retain cycles using weak or unowned references.

Both avoid retain cycles by not increasing the reference count. A weak reference becomes nil automatically when its target is deallocated, so it must be optional. An unowned reference assumes the target outlives it and does not become nil, so accessing it after deallocation crashes.

Actors protect their mutable state by ensuring only one task accesses it at a time, serializing access automatically. This prevents data races in concurrent code, so instead of manually locking, you model shared mutable state as an actor and interact with it through await.

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