Swift 有没有一种方法可以访问封闭实例ObservableObject以从属性包装器中的任何位置调用objectWillChange.send()

我正在try 创建一个类似于Combine的Published的属性包装器(用于我的项目需要)，但能够通过向发布者发送存储在projectedValue中的值来修改包装的属性，如下所示:

// in class
@PublishedMutable var foo = "foo"

$foo.send("bar")
// ...

以下是属性包装的代码:

@propertyWrapper
struct PublishedMutable<Value> {
    static subscript<T: ObservableObject>(
        _enclosingInstance instance: T,
        wrapped wrappedKeyPath: ReferenceWritableKeyPath<T, Value>,
        storage storageKeyPath: ReferenceWritableKeyPath<T, Self>
    ) -> Value {
        get {
            instance[keyPath: storageKeyPath].storage
        }
        set {
            let publisher = instance.objectWillChange
            // This assumption is definitely not safe to make in
            // production code, but it's fine for this demo purpose:
            (publisher as? ObservableObjectPublisher)?.send()
            
            instance[keyPath: storageKeyPath].storage = newValue
        }
    }
    
    @available(*, unavailable,
                message: "@PublishedMutable can only be applied to classes"
    )
    var wrappedValue: Value {
        get { fatalError() }
        set { fatalError() }
    }
    
    private var storage: Value{
        get { publisher.value }
        set { publisher.send(newValue) }
    }
    typealias Publisher = CurrentValueSubject<Value, Never>

    var projectedValue: Publisher { self.publisher }

    private var publisher: Publisher
    init(initialValue: Value) {
        self.publisher = Publisher(initialValue)
    }
    
    init(wrappedValue: Value) {
        self.init(initialValue: wrappedValue)
    }
}

下面是我用来测试其功能的playground 代码:

class AmogusComic: ObservableObject {
    @PublishedMutable var currentPageContent = "S O S"
    
    private var cancellables: Set<AnyCancellable> = []
    
    func connect() {
        $currentPageContent.sink { newPage in
            print(newPage)
        }
        .store(in: &cancellables)
        objectWillChange.sink { _ in
            print("Update")
        }
        .store(in: &cancellables)
    }
}

let amogusComic = AmogusComic()
DispatchQueue.main.async {
    // connect publishers and print initial content. prints "S O S"
    amogusComic.connect()
    
    // change the value of current page via setting a property, the amogusComic class will reactively print "S U S" after
    amogusComic.currentPageContent = "S U S"
    
    // take a property publisher and send new value to publisher, the amogusComic class will reactively print "A M O G U S" after
    amogusComic.$currentPageContent.send("A M O G U S")
}

PlaygroundPage.current.needsIndefiniteExecution = true

只需通过直接修改属性和将值发送到Publisher来修改值就可以完美地工作. 但我也想在任何时候值发生变化时呼叫objectWillChange.send() 问题是，只有在直接修改包装属性时才会调用它，这是不正确的行为.

测试代码输出如下

S O S
Update
S U S
A M O G U S

当我认为它应该输出这个

S O S
Update
S U S
Update
A M O G U S

正如您在上面的代码中看到的，我使用_enclosingInstance个静态下标来获取ObservableObject并调用objectWillChange，但事实证明，只有在直接修改属性时，SWIFT才会调用该下标(amogusComic.currentPageContent = "S U S")

得到Mirror(reflecting: self).superclassMirror也不起作用，superclassMirror总是返回零

我能不能得到_enclosingInstance静态下标之外的ObservableObject？因此，我还可以在将值发送到发布者时调用objectWillChange