I’m curious if anyone has found a way to use associated objects within Swift’s strict concurrency model. The objective c based function calls (objc_setAssociatedObject and objc_getAssociatedObject) have a const void *key argument. Typically, this is obtained by having a private global variable which is passed as an inout argument.
E.g.
private var myKey: Void?
extension MyProtocol {
var myAddedString: String? {
get {
objc_getAssociatedObject(self, &myKey) as? String
}
set {
objc_setAssociatedObject(self, &myKey, newValue, .OBJC_ASSOCIATION_COPY)
}
}
}
This approach does not appear to be compatible with Swift strict concurrency, though, because myKey is “non-isolated global shared mutable state”. I can’t change the var to be a let, which would solve the concurrency issue, as then it can’t be used as an inout argument.
I’m curious if anyone has found a way around this other than binding myKey to a global actor.
1
You don’t need a var and & to get a UnsafeRawPointer – you can just create one with init(bitPattern:):
let myKey = UnsafeRawPointer(bitPattern: 1)!
This does not guarantee that the key is unique, however.
To get a unique value, we can declare a type, and get the ObjectIdentifier of that type.
enum MyKey {}
let myKey = UnsafeRawPointer(bitPattern: Int(bitPattern: ObjectIdentifier(MyKey.self)))!
get {
// do not write '&' here!
objc_getAssociatedObject(self, myKey) as? String
}
2
You can make the key nonisolated(unsafe) given that you’re not mutating it (and neither do objc_getAssociatedObject nor objc_setAssociatedObject)). It’s just using the address. So:
private nonisolated(unsafe) var myKey: Void?