Array of methods in swift without reference cycle

Question

My goal is to create a class which contains an array. The elements of the array will be the methods of the same class. like:

class MyClass {
    lazy var functions = [self.myFirstMethod, self.mySecondMethod]

    deinit {
        print("Deinit")
    }

    func myFirstMethod() {
        // Do Something
    }

    func mySecondMethod() {
        // Do Something
    }

    func executeAll() {
        for f in functions {
            f()
        }
    }
}

When I call the executeAll() it works fine and I achieve my expected result:

var myObject = MyClass()
myObject.executeAll()

The problem is, it create reference cycle. Instance of MyClass holds the array functions and functions array holds self. So If I write below code:

var myObject: MyClass? = MyClass()
myObject.executeAll()
myObject = nil

It will not call deinit method because of this strong reference cycle. How can I add method pointers to array as weak self? I don't want to use a local copy of functions in executeAll method.

why not just declare your functions variable as optional, and simply set it to nil after the execution since you want it to be deallocated after. — koropok
– koropok, Commented Mar 7, 2019 at 8:12

Martin R · Accepted Answer · 2019-03-07 08:10:11Z

2

If the method list is independent of the particular instance then you can make it a type property and avoid the reference cycle:

class MyClass {
    static let functions = [myFirstMethod, mySecondMethod]

    func executeAll() {
        for f in MyClass.functions {
            f(self)()
        }
    }

   // ...
}

The array elements are “curried functions” of the type

(MyClass) -> () -> ()

compare Instance Methods are “Curried” Functions in Swift.

edited Mar 7, 2019 at 8:10

answered Mar 7, 2019 at 8:04

Martin R

541k98 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Mohmmad S · Accepted Answer · 2019-03-07 08:08:50Z

-1

Try this way,

class Unowned<T: AnyObject> {
    unowned let value: T
    init(_ value: T) {
        self.value = value
    }
}

var myObject: MyClass = MyClass()
var myUnowned = Unowned(myObject)
myUnowned.value.executeAll()

answered Mar 7, 2019 at 8:08

Mohmmad S

5,1085 gold badges22 silver badges52 bronze badges

5 Comments

Martin R Over a year ago

I am afraid that this would not solve the retain cycle problem. If you set myObject = nil after calling myUnowned.value.executeAll() the the object is not deallocated. And if you set myObject = nil before calling myUnowned.value.executeAll() then you'll get a crash.

Mohmmad S Over a year ago

Are you doing that on playground ?

Martin R Over a year ago

No, in a compiled project. A Playground is not good for testing object (de)allocation.

Mohmmad S Over a year ago

i know, was making sure you're not

Martin R Over a year ago

Try let myUnowned = Unowned(MyClass()); myUnowned.value.executeAll() ... 💣

Collectives™ on Stack Overflow

Array of methods in swift without reference cycle

2 Answers 2

Comments

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related