Swift Tutorials: Strong References 🎯

Welcome back! In this lesson, we'll dive deep into Swift's strong references. Let's begin! 🚀

What are Strong References? 📝

Strong references in Swift are connections between two variables that keep an object alive in memory. When a strong reference exists, the object is not deallocated (or destroyed) until the last strong reference to it is removed.

Let's visualize it with an example:

swift

class Car {
    var model: String

    init(model: String) {
        self.model = model
        print("Car created: \(model)")
    }
}

var car1 = Car(model: "Tesla")
var car2 = car1 // Strong reference created between car1 and car2

// Car created: Tesla

car1 = Car(model: "BMW") // car1's reference is now pointing to a new object, but car2 still points to the original "Tesla" object.

// Car created: BMW
// Car created: Tesla (This is because car2 still points to the original "Tesla" object)

Strong Reference Lifecycle 📝

When a new object is created, Swift automatically assigns it a strong reference.
Strong references can be shared between variables, classes, or functions.
As long as there's at least one strong reference to an object, the object remains in memory.
When all strong references to an object are removed, the object is deallocated (or destroyed) by Swift.

Retaining Cycles and Memory Leaks 💡

Be aware of retaining cycles that can lead to memory leaks. A retaining cycle occurs when two objects maintain strong references to each other, keeping both of them alive in memory even when they are no longer needed.

Let's see an example of a retaining cycle:

swift

class Person {
    var name: String
    var car: Car?

    init(name: String) {
        self.name = name
        print("\(name) created")
    }
}

class Car {
    var owner: Person?

    init(owner: Person) {
        self.owner = owner
        owner.car = self
        print("Car created for \(owner.name)")
    }
}

var john = Person(name: "John")
var carJohn = Car(owner: john)

// John created
// Car created for John

// If john and carJohn are no longer needed, they will still remain in memory because of the retaining cycle.

// To break the cycle, set the owner property to nil when the car is no longer needed:
carJohn.owner = nil

Stay tuned for the next lesson on weak and unowned references! 🎓