The following code currently has a retain cycle and memory leak:
enum ParentChild {
case SonOf(Parent)
case DaughterOf(Parent)
}
class Parent {
lazy var son: Child = Child(parentChild: .SonOf(self))
lazy var daughter: Child = Child(parentChild: .DaughterOf(self))
deinit { print("deinit Parent") }
}
class Child {
var parentChild: ParentChild
init(parentChild: ParentChild) {
self.parentChild = parentChild
}
deinit { print("deinit Child") }
}
do {
let parent = Parent()
parent.son
parent.daughter
}
Child.parentChild cannot be declared unowned because ParentChild is a value
type. I propose adding the ability to declare the reference storage class for
an enum's associated value, like so:
enum ParentChild {
case SonOf(unowned Parent)
case DaughterOf(unowned Parent)
}
The only current alternative is to have some intermediate reference type that
itself holds the reference, akin to the old "Box" type that we used to use to
work around enum limitations. E.g., this is our current cumbersome work-around:
/// An unowned reference to a value, which is useful for maintaining
parent-child relations through value types like enums
public struct UnownedRef<T: AnyObject> {
public unowned let value: T
public init(_ value: T) { self.value = value }
}
enum ParentChild {
case SonOf(UnownedRef<Parent>)
case DaughterOf(UnownedRef<Parent>)
}
class Parent {
lazy var son: Child = Child(parentChild: .SonOf(UnownedRef(self)))
lazy var daughter: Child = Child(parentChild: .DaughterOf(UnownedRef(self)))
deinit { print("deinit Foo") }
}
class Child {
var parentChild: ParentChild
init(parentChild: ParentChild) {
self.parentChild = parentChild
}
deinit { print("deinit Child") }
}
The storage type of an enum would, of course, be limited to reference types,
and when the storage class is weak, it would require that the stored type be
Optional, just like when declaring a weak variable.
What do people think?
-Marc
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