How would you avoid retain cycles when using closures/blocks in Swift?

Retain cycles can occur when using closures or blocks in Swift because closures and blocks capture a strong reference to the objects they reference, and if an object captures a strong reference to a closure that references the object, a retain cycle can occur. To avoid retain cycles when using closures or blocks in Swift, you can use one or more of the following techniques:

1. Capture self weakly or unowned: When a closure captures self, it can lead to a retain cycle. To avoid this, you can capture self weakly or unowned in the closure. This means that the closure will hold a weak reference to self, and if self is deallocated, the closure will automatically become nil. Here's an example:

class MyClass {
    var myClosure: (() -> Void)?

    func myFunc() {
        myClosure = { [weak self] in
            self?.doSomething()
        }
    }

    func doSomething() {
        // ...
    }
}

2. Use a capture list to break the retain cycle: You can use a capture list to specify which variables a closure should capture weakly or unowned. This allows you to explicitly control the lifetime of the captured variables, which can help prevent retain cycles. Here’s an example:

class MyClass {
    var myClosure: (() -> Void)?

    func myFunc() {
        myClosure = { [weak self] in
            guard let strongSelf = self else { return }
            strongSelf.doSomething()
        }
    }

    func doSomething() {
        // ...
    }
}

3. Use a capture group to break the retain cycle: You can use a capture group to capture a group of variables weakly or unowned together. This allows you to explicitly control the lifetime of the captured variables as a group, which can help prevent retain cycles. Here’s an example:

class MyClass {
    var myClosure: (() -> Void)?

    func myFunc() {
        myClosure = { [weak self, weak myObject = self.myObject] in
            guard let strongSelf = self, let strongMyObject = myObject else { return }
            strongSelf.doSomething(with: strongMyObject)
        }
    }

    var myObject: MyObject?

    func doSomething(with object: MyObject) {
        // ...
    }
}

By using one or more of these techniques, you can avoid retain cycles when using closures or blocks in Swift.