竞态条件与递归问题：字典未在执行下一行前返回

• 以fixedValues作为dictionaryRepresentation参数初始化MyClass。
• 在执行init代码行前设置好修正后的值。

• fixedValues在执行self.init(...代码行前未完成设置。

• 使用返回值替代completion（当前状态）
• 利用completion、DispatchGroups、Notify
• 使用Semaphore等待值设置

class WaitForValue {
    private var semaphore = DispatchSemaphore(value: 0)
    
    var valueToWaitFor: String? {
        didSet {
            if valueToWaitFor != nil {
                semaphore.signal()
            }
        }
    }
    
    func waitForValue() {
        _ = semaphore.wait(timeout: .distantFuture)
    }
}

let waitForValueInstance = WaitForValue()

// 会阻塞直到valueToWaitFor被设置为非nil值
DispatchQueue.global().async {
    waitForValueInstance.waitForValue()
    print("Value received: \(waitForValueInstance.valueToWaitFor ?? "nil")")
}

// 模拟延迟后设置值
DispatchQueue.global().asyncAfter(deadline: .now() + 2) {
    waitForValueInstance.valueToWaitFor = "Hello, World!"
}

class MyClass {

    convenience init?(_ object: Object) {
        
        guard let values = object.getValues(forKeys: MyAttributes.allAttributes) else { return nil }
        
        var fixedValues = values
        
        MyClass.correctedValues(object: object, values: values) { correctedValues in
            fixedValues = correctedValues
        }
        
        self.init(dictionary: fixedValues, type: object.type)
    }

    private static func correctedValues(object: Object, values: [String: Any], completion: @escaping([String: Any]) -> Void) {
        
        var valuesDictionary = values
        
        let fixes = objectFixes(object: object)
        
        let valueObjects = values["children"] as? [Object] ?? []
        var wrappedObjects = [WrappedObject]()
        valueObjects.forEach {
            let wrapped = WrappedObject($0)
            wrappedObjects.append(wrapped)
        }
        
        fixedChildrenValues(originalValues: wrappedObjects, fixes: fixes) { correctedChildren in
            valuesDictionary["children"] = correctedChildren
            completion(valuesDictionary)
        }
    }

    private static func fixedChildrenValues(originalValues: [WrappedObject], fixes: [String: [Attribute: String]], completion: @escaping ([[String: Any]]) -> Void) {
        
        var fixedChildrenArray = [[String: Any]]()
        
        for childValue in originalValues {
            
            var childAttributes = childValue.getValues(forKeys: [
                "children",
                "identifier",
                "props",
                "name"
            ]) ?? [:]
            
            // 应用修正
            if let matchingIdentifier = childAttributes["identifier"] as? String,
               let fix = fixes[matchingIdentifier] {
                fix.forEach { (key, value) in
                    childAttributes[key] = value
                }
            }
            
            // 尝试提取子元素并继续遍历
            if let childrenObjects = childAttributes["children"] as? [Object] {
                var wrappedObjects = [WrappedObject]()
                for childObject in childrenObjects {
                    wrappedObjects.append(WrappedObject(childObject))
                }

                if !wrappedObjects.isEmpty {
                    fixedChildrenValues(originalValues: wrappedObjects, fixes: fixes) { correctedChildren in
                        childAttributes["children"] = correctedChildren
                        fixedChildrenArray.append(childAttributes)
                    }
                } else {
                    fixedChildrenArray.append(childAttributes)
                }
            } else {
                fixedChildrenArray.append(childAttributes)
            }
        }
        
        completion(fixedChildrenArray)
    }

    private static func objectFixes(object: Object) -> [String: [Attribute: String]] {
        var objectFixes = [String: [Attribute: String]]()
        let objects = object.objects
        
        for i in 0..<objects.count {
            let obj = objects[i]
            if !obj.isEnabled {
                objectFixes[obj.identifier] = ["props": "false"]
            }
        }
        
        return objectFixes
    }
}

内容的提问来源于stack exchange，提问作者Tristan Newman