Quick Answer: What Is A Weak VAR In Swift?

What is difference between weak and strong in Swift?

A strong reference means that you want to “own” the object you are referencing with this property/variable.

In contrast, with a weak reference you signify that you don’t want to have control over the object’s lifetime.

A weak reference is like observing the tree from afar.


What is the difference between weak and unowned?

The first difference you need to know about is that an unowned reference is always expected to have a value. … When that happens, the reference is set to nil . Because a weak reference can be set to nil , it is always declared as an optional. That is the second difference between weak and unowned references.

What is strong reference in Swift?

Strong Reference Cycle. In essence, strong references are used to describe the relationship between objects. When an object has a strong reference to another object, this creates a retain cycle that prevents the object that is being referenced from being deallocated and increases the retain count to 1.

What is unowned self in Swift?

The most common place you’ll see unowned variables is with closures that declare [unowned self] – this means “I want to reference self inside this closure but I don’t want to own it.” Why unowned rather than weak ? Both would work, but let’s face it: if self is nil inside a closure, something has gone wrong!

Why are delegates weak?

The reason that objects weakly retain their delegates is to avoid retain cycles. Imagine the following scenario: object a creates b and retains it, then sets itself as b ‘s delegate. a is released by its owner, leaving a retain cycle containing a and b . This is actually a very common scenario.

Why we use delegates in Swift?

Delegation is used for everything from handling table view events using UITableViewDelegate , to modifying cache behavior using NSCacheDelegate . The core purpose of the delegate pattern is to allow an object to communicate back to its owner in a decoupled way.

What does @escaping do Swift?

In short, @escaping is used to inform callers of a function that takes a closure that the closure might be stored or otherwise outlive the scope of the receiving function. This means that the caller must take precautions against retain cycles and memory leaks. It also tells the Swift compiler that this is intentional.

Why is IBOutlet weak?

In Mac development an IBOutlet is usually a weak reference: if you have a subclass of NSViewController only the top-level view will be retained and when you dealloc the controller all its subviews and outlets are freed automatically. UiViewController use Key Value Coding to set the outlets using strong references.

Why delegates are weak in Swift?

With using lazy keyword we are not initializing delegate which means there is no memory leak right now. Let’s break that. Object will be created and there will be memory leak. … Therefore, if the object conforming to the protocol needs to be stored in a weak property then the protocol must be a class-only protocol.

What is a lazy VAR in Swift?

Swift has a mechanism built right into the language that enables just-in-time calculation of expensive work, and it is called a lazy variable. These variables are created using a function you specify only when that variable is first requested.

What is computed property in Swift?

Swift offers us two kinds of property: a stored property is one that saves a value for use later, and a computed property is one that runs some code in order to calculate the value. … The computed property returns a string based on joining the four stored properties into a sentence.

What is a retain cycle Swift?

What are retain cycles and memory leaks? A memory leak in iOS is when an amount of allocated space in memory cannot be deallocated due to retain cycles. Since Swift uses Automatic Reference Counting (ARC), a retain cycle occurs when two or more objects hold strong references to each other.

Why we use lazy in Swift?

Lazy properties are also useful when the initial value for a property requires complex or computationally expensive setup that shouldn’t be performed unless or until it’s needed. The example below uses a lazy stored property to avoid unnecessary initialization of a complex class.

What is optional in Swift?

An optional in Swift is basically a constant or variable that can hold a value OR no value. The value can or cannot be nil. It is denoted by appending a “?” after the type declaration. … This is a big impact on the language Swift itself because what that means is that anything non-optional types can never be nil.

What is the difference between weak and strong?

A variable that does not take ownership of an object is known as a weak reference. strong is the default. An object remains “alive” as long as there is a strong pointer to it. … A weak reference is set to nil when there are no strong references to the object.

What are closures in Swift?

Closures are self-contained blocks of functionality that can be passed around and used in your code. Closures in Swift are similar to blocks in C and Objective-C and to lambdas in other programming languages. … Nested functions are closures that have a name and can capture values from their enclosing function.