Reference cycles with value types?

Question

Reference cycles in Swift occur when properties of reference types have strong ownership of each other (or with closures).

Is there, however, a possibility of havin

Answer 1

You normally cannot have a reference cycle with value types simply because Swift normally doesn't allow references to value types. Everything is copied.

However, if you're curious, you actually can induce a value-type reference cycle by capturing self in a closure.

The following is an example. Note that the MyObject class is present merely to illustrate the leak.

class MyObject {
    static var objCount = 0
    init() {
        MyObject.objCount += 1
        print("Alloc \(MyObject.objCount)")
    }

    deinit {
        print("Dealloc \(MyObject.objCount)")
        MyObject.objCount -= 1
    }
}

struct MyValueType {
    var closure: (() -> ())?
    var obj = MyObject()

    init(leakMe: Bool) {
        if leakMe {
            closure = { print("\(self)") }
        }
    }
}

func test(leakMe leakMe: Bool) {
    print("Creating value type.  Leak:\(leakMe)")
    let _ = MyValueType(leakMe: leakMe)
}

test(leakMe: true)
test(leakMe: false)

Output:

Creating value type.  Leak:true
Alloc 1
Creating value type.  Leak:false
Alloc 2
Dealloc 2