我有一个Swift协议(protocol)定义如下:protocolSmartContract{funcapply(transaction:Transaction)funcaddBrokenRule(_brokenRule:BrokenRule)varbrokenRules:[BrokenRule]{getset}}我在SmartContract上有一个扩展，定义如下:extensionSmartContract{mutatingfuncaddBrokenRule(_brokenRule:BrokenRule){ifself.brokenRules==nil{self.brokenRu