- Set a Reference to “nil” Let’s check out setting to nil first, because it’s the simplest to work with. …
- Mark a Reference as “weak” The more complicated alternative to fixing a strong reference cycle is marking a reference as weak.
How do you avoid reference cycle?
To break the strong reference cycle between an Account instance and a Plan instance, we
declare the account property of the Plan class as weak
. Remember that this has a few consequences. We need to declare the account property as a variable property and it needs to be of an optional type.
What is a strong reference cycle?
A strong reference cycle is when two instances of classes reference each other without the proper safeties ( weak / unowned ) hence preventing the garbage collector from disposing of them once all the variables I created stopped referencing those objects.
How do you resolve a strong reference cycle in closures?
You resolve a strong reference cycle between a closure and a class instance by
defining a capture list as part of the closure’s definition
. A capture list defines the rules to use when capturing one or more reference types within the closure’s body.
Can unowned be optional?
Difference between weak reference and unowned reference
The weak reference is an optional type, which means weak reference will set to nil once the instance it refers to frees from memory. On the other hand,
unowned reference is a non-optional type
, it never will be set to nil and always have some value.
Does Swift have a garbage collector?
Unlike other programming languages like Java or Kotlin,
Swift doesn’t have a garbage collector
. Instead, it uses a much faster technique called Automatic Reference Counting (ARC). In most cases, this means you don’t have to worry about memory handling in Swift. It simply works, as if it were a garbage collector.
What is a strong reference Swift?
In Swift, a strong reference is
the default, for variables, properties, constants, passing into functions (depending on what you do with it), and for closures
. With ARC, an instance is only deallocated when its retain count is zero. A strong reference increases the retain count by 1, a weak reference does not.
What is unowned reference in Swift?
Unowned references are similar to weak references in that
they don’t keep a strong reference to the instance they are referencing
. They serve the same purpose as weak references, that is, they avoid strong reference cycles.
What is a strong reference?
Strong References: This is
the default type/class of Reference Object
. Any object which has an active strong reference are not eligible for garbage collection. The object is garbage collected only when the variable which was strongly referenced points to null.
What is strong weak and unowned in Swift?
The key difference between a strong and a weak or unowned reference is that
a strong reference prevents the class instance it points to from being deallocated
. That is very important to understand and remember. ARC keeps track of the number of strong references to a class instance.
What is a reference cycle?
A reference cycle simply means
one or more objects referencing each other
, such that if you drew it out on paper with arrows representing the dependencies you would see a cycle. The (almost) simplest reference cycle is having two objects a and b that refer to each other: a.other = b b.some_attr = a.
What is weak VAR in Swift?
Weak References in Swift
Weak References are one solution to retain cycles in Swift.
A weak reference does not increment or decrement the reference count of an object
. Since weak references do not increment the reference count of an object, a weak reference can be nil .
Is ARC a garbage collection?
ARC differs from tracing garbage collection in that there is no background process that deallocates the objects asynchronously at runtime
. Unlike tracing garbage collection, ARC does not handle reference cycles automatically.
What is memory leak in Swift?
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 delegates are weak in Swift?
Why delegate should be weak var? Before you begin I highly recommend you to check ARC story. We will design protocol and classes in order to show retain cycle on delegates.
With using lazy keyword we are not initializing delegate which means there is no memory leak right now
.
Why outlets are weak in Swift?
Outlets that you create will therefore typically be weak by default, because:
Outlets that you create to, for example, subviews of a view controller’s view or a window controller’s window, are arbitrary references between objects that do not imply ownership
.
What is closure Swift?
In Swift, a closure is
a special type of function without the function name
. For example, { print(“Hello World”) } Here, we have created a closure that prints Hello World .
Does iOS use garbage collection?
Memory management in Swift (iOS)
Swift uses a simple garbage collection mechanism
. It’s called ARC (Automatic Reference Counting). This approach is based on tracking the strong references count to an object held by other objects.
Does kotlin use GC?
Kotlin/Native garbage collector
The original Kotlin/Native automatic memory manager uses a deferred reference-counting garbage collector
. We chose it for its simplicity – not because of its memory consumption.
Does Java garbage collection use reference counting?
Because
the garbage collector in modern JVMs is no longer tracking references count
. This algorithm is used to teach how GC works, but it was both resource-consuming and error-prone (e.g. cyclic dependencies).
What optional binding?
Optional Binding is
used to safely unwrap the optional value
. Step one: We assign our optional value to temporary constant & variable. Step Two: If the optional variable contains a value it will be assigned to our temporary variable.
Why we use lazy in Swift?
Lazy variables
allow you to delay the initialisation of stored properties
. This can be useful to only perform expensive work when it’s actually needed. The different between lazy- and computed properties is important in cases you need to have calculations based on the current state of values.
What is optional in Swift?
An Optional is
a type on its own, actually one of Swift 4’s new super-powered enums
. It has two possible values, None and Some(T), where T is an associated value of the correct data type available in Swift 4.
When should I use strong weak unowned?
So when do we use them?! According to Apple’s docs: “
Use a weak reference whenever it is valid for that reference to become nil at some point during its lifetime
. Conversely, use an unowned reference when you know that the reference will never be nil once it has been set during initialization.”
Can unowned be nil?
However, weak variables can become nil – they are effectively optional. In comparison,
unowned variables must never be set to nil once they have been initialized
, which means you don’t need to worry about unwrapping optionals.
What is weak and unowned IOS?
The main difference between weak and unowned is that
weak is optional while unowned is non-optional
. By declaring it weak you get to handle the case that it might be nil inside the closure at some point. If you try to access an unowned variable that happens to be nil, it will crash the whole program.
