In Swift, weak and unowned are two keywords that you can use to define a reference to an object. Both weak and unowned references are used to avoid strong reference cycles, which can cause memory leaks in your program.
A weak reference is a reference to an object that does not prevent the object from being deallocated. This means that the object can be deallocated if there are no other strong references to it. A weak reference is set to nil when the object it refers to is deallocated.
An unowned reference, on the other hand, is a reference to an object that does not keep the object alive. This means that the object can be deallocated at any time, and the unowned reference will not be set to nil. If you try to access an object through an unowned reference after it has been deallocated, your program will crash.
Here are a few key points to remember about weak and unowned references:
weak references are useful when the reference object may become nil at some point in the future. This is often the case when the reference object is owned by another object, and the reference object may be deallocated if the owning object is deallocated first.
unowned references are useful when the reference object is guaranteed to always be alive while the referencing object is alive. This is often the case when the reference object and the referencing object have a parent-child relationship, and the reference object is guaranteed to outlive the referencing object.
You should use weak references whenever possible, as they are safer than unowned references. Unowned references can lead to crashes if the reference object is deallocated before the referencing object.