Delete an instance of a class in Swift

Question

How can I delete an instance of a class in Swift? Looking for some kind of equivalent to

del instance

in Python. I'm pretty new to Swift, and I couldn't find anything in the documentation or any prior posts.

I have a bullet class in a game that needs to be deleted after colliding with a player. Example code could go something like

class Bullet() {
    init() {
        for traveled in 0...range {
            //travel forward
            if collided {
                //damage collided player
                del self
    }
}

Edit: This is what cleared it up for me http://www.apeth.com/iOSBook/ch12.html#_memory_management

Please update your question with some relevant Swift code. Clearly explain what you are trying to do. — rmaddy, Jul 29 '18 at 17:42
It isn't obvious that `del` does anything useful even in Python; see https://stackoverflow.com/questions/6146963/when-is-del-useful-in-python. What problem are you actually having? — matt, Jul 29 '18 at 17:44
@EvanC "Are you saying that if the compiler sees no more strong references to an instance in the rest of the code, it automatically "deallocates" (which I assume is equivalent to del) that instance?" Almost! Not the compiler; the runtime. Swift uses ARC (automatic reference counting). Might want to read my explanation here: http://www.apeth.com/iOSBook/ch12.html#_memory_management — matt, Jul 29 '18 at 18:12

George · Answer 1 · 2018-07-29T18:58:27.073

Swift, as mentioned in another question, uses Automatic Reference Counting.

Apple explains it like this:

ARC tracks how many properties, constants, and variables are currently referring to each class instance. ARC will not deallocate an instance as long as at least one active reference to that instance still exists.

ARC in Action

Here’s an example of how Automatic Reference Counting works. This example starts with a simple class called Person, which defines a stored constant property called name:

class Person {
    let name: String

    init(name: String) {
        self.name = name
        print("\(name) is being initialized")
    }

    deinit {
        print("\(name) is being deinitialized")
    }
}

The Person class has an initializer that sets the instance’s name property and prints a message to indicate that initialization is underway. The Person class also has a deinitializer that prints a message when an instance of the class is deallocated.

The next code snippet defines three variables of type Person?, which are used to set up multiple references to a new Person instance in subsequent code snippets. Because these variables are of an optional type (Person?, not Person), they are automatically initialized with a value of nil, and do not currently reference a Person instance.

var reference1: Person?
var reference2: Person?
var reference3: Person?

You can now create a new Person instance and assign it to one of these three variables:

reference1 = Person(name: "John Appleseed")
// Prints "John Appleseed is being initialized"

Note that the message "John Appleseed is being initialized" is printed at the point that you call the Person class’s initializer. This confirms that initialization has taken place.

Because the new Person instance has been assigned to the reference1 variable, there is now a strong reference from reference1 to the new Person instance. Because there is at least one strong reference, ARC makes sure that this Person is kept in memory and is not deallocated.

If you assign the same Person instance to two more variables, two more strong references to that instance are established:

reference2 = reference1
reference3 = reference1

There are now three strong references to this single Person instance.

If you break two of these strong references (including the original reference) by assigning nil to two of the variables, a single strong reference remains, and the Person instance is not deallocated:

reference1 = nil
reference2 = nil

ARC does not deallocate the Person instance until the third and final strong reference is broken, at which point it’s clear that you are no longer using the Person instance:

reference3 = nil
// Prints "John Appleseed is being deinitialized"

All code and writing for ARC in Action is from Apple's documentation.

Duncan C · Accepted Answer · 2018-07-29T18:23:13.583

3

Your question doesn't make a lot of sense in Swift. Swift uses ARC (Automatic Reference Counting) to manage object lifecycles.

As long as you maintain at least one strong reference to an object, it lives. As soon as there are no more strong references, it gets deallocated.

Consider the following code.

class FooClass {
   var value: Int
}
var foo: FooClass?


foo = FooClass(value: 3)    


//foo will be valid

foo = nil; //This causes the object in `foo` to be deallocated immediately.

The closest thing to del (assuming I understand what it does - I don't know Python) seems like assigning nil to an optional var, assuming there are no other strong references to the object.

edited Jul 29 '18 at 18:23

answered Jul 29 '18 at 17:57

Duncan C

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Thanks for the response. I just updated my question with some example code, that should clarify my intention. I'm pretty confused though... this is also my first time learning a compiled language, it could have to do with that. Are you saying that if the compiler sees no more strong references to an instance in the rest of the code, it automatically "deallocates" (which I assume is equivalent to del) that instance? – Evan C Jul 29 '18 at 18:07
1

ARC doesn't apply to value types such as `String`. – rmaddy Jul 29 '18 at 18:11

Delete an instance of a class in Swift

2 Answers2

ARC in Action