将核心数据类作为最终类以满足协议“自我”要求

Posted 2023-03-05

【中文标题】将核心数据类作为最终类以满足协议“自我”要求

【英文标题】：Making the Core Data class as final to satisfy the protocol 'Self' requirement

【发布时间】：2017-11-28 20:18:18

【问题描述】：

我编写了一个协议，允许将简单链中的对象与前任和后继联系起来。

我正在尝试将此协议与我的核心数据实体“事件”一起使用，但出现此错误：

错误：

Protocol 'Chainable' requirement 'chain' cannot be satisfied by a non-final class ('Event') because it uses 'Self' in a non-parameter, non-result type position.

如何使这个类final（我不想将 Codegen 设置为手动），或者重写 var chain: [Self] 定义？

提前谢谢你。

extension Event: Chainable 

protocol Chainable where Self: NSManagedObject 

    var chain: [Self]  get 

    var predecessor: Self?  get set 
    var successor: Self?  get set 

    var selfIndexInChain: Int  get 

    mutating func moveInChain(to index: Int)
    mutating func removeSelfFromChain()

    mutating func addSelfAsSuccessor(of object: Self)
    mutating func addSelfAsPredecessor(of object: Self)


extension Chainable 
   
    var chain: [Self] 
    
        var _chain: [Self] = [self]
    
        // go right
        var current: Self = self
        while let successor = current.successor 
        
            _chain.append(successor)
            current = successor
        
    
        // go left
        current = self
        while let predecessor = current.predecessor 
        
            _chain.insert(predecessor, at: 0)
            current = predecessor
        
    
        // TODO: - Compare speed with the alternative realization: Find the first element, then populate the tasks array.
    
        return _chain
    

    // Self Index in the chain
    var selfIndexInChain: Int  return self.chain.index(of: self)! 


    // Change place in the cahain
    mutating func moveInChain(to index: Int) 
    
        guard index != selfIndexInChain else  return  // Check the index isn't same
        guard 0...(chain.count-1) ~= index else  return 
    
        let taskAtDestination = chain[index]
    
        if index > selfIndexInChain 
        
            removeSelfFromChain()
            addSelfAsSuccessor(of: taskAtDestination)
        else 
            removeSelfFromChain()
            addSelfAsPredecessor(of: taskAtDestination)
       
    

    mutating func removeSelfFromChain() 
    
        let successor = self.successor
        let predecessor = self.predecessor
    
        self.predecessor = nil
        self.successor = nil
    
        self.predecessor?.successor = successor
        self.successor?.predecessor = predecessor
    

    mutating func insertSelfBetween(lhs: Self, rhs: Self) 
        // self shouldn't be linked
        guard self.predecessor == nil && self.successor == nil else  return 
    
        guard (lhs.successor == rhs && rhs.predecessor == lhs) ||
            (lhs.successor == nil && rhs.predecessor == nil ) else  return  // If both are nil, they will be connected thru self
    
        self.predecessor = lhs
        self.successor = rhs
    
    

    mutating func addSelfAsSuccessor(of object: Self) 
        // self shouldn't be linked
        guard self.predecessor == nil && self.successor == nil else  return  // TODO: Add error support
        // self shouldn't be already the successor 
        guard object.successor != self else  return 
    
        let previousSuccessor = object.successor
        self.predecessor = object
        self.successor = previousSuccessor
    
    

    mutating func addSelfAsPredecessor(of object: Self) 
        // self shouldn't be linked
        guard self.predecessor == nil && self.successor == nil else  return 
        // self shouldn't be the task successor already
        guard object.predecessor != self else  return 
    
        let previousPredecessor = object.predecessor
        self.successor = object
        self.predecessor = previousPredecessor
    

【参考方案1】：

我也遇到了类似的问题。

解决方法：

查看您的代码，Chainable 似乎将由多个 NSManagedObject 子类实现。

用Chainable 代替Self 并让Chainable 包含需要与NSManagedObject 子类通用的最低要求。

在某些情况下，这意味着为 NSManagedObject 子类实现的某些功能实现包装器