swift - 如何克服 "Generic parameter ' T' is not used in function signature”的错误？

Question

我正在尝试将以下内容转换为通用内容。

extension RLMOrganization: DataProvider {

    func getLastSyncToken() -> String {
        let lastUpdated: RLMOrganization? = self.findAll(sortedBy: "syncToken").last

        if let syncToken = lastUpdated?.syncToken {
            return syncToken
        } else {
            return "00000000000000000000000000000000"
        }
    }


}

并试过这个:

protocol DataProvider: DatabaseLayer {
    associatedtype T: Object

    func findAll<T: Object>(sortedBy key: String) -> [T]
}

extension DataProvider {

func findAll<T: Object>(sortedBy key: String) -> [T] {
    let database = self.getDatabase()

    if let allObjects = database?.objects(T.self) {
        let results = allObjects.sorted(byKeyPath: key, ascending: true)
        return Array(results)
    }

    return []
}


    func getLastSyncToken<T: Object>() -> String {
        let lastUpdated = self.findAll(sortedBy: "syncToken").last as? T

        if let value = lastUpdated?.value(forKey: "syncToken") {  // get value from object by string name
            let syncToken = value as! String
            return syncToken
        } else {
            return "00000000000000000000000000000000"
        }
    }

...

但似乎无法克服以下错误:

Generic parameter 'T' is not used in function signature

我认为编译器拥有确定类型用法所需的一切。

Answer 1

下面对我有用，我不知道如何findAll已定义，但问题是我看到的对 self 的引用，因此您需要使用 associatedtype 在那里定义 T .

protocol DataProvider: DatabaseLayer {
    associatedtype T: Object

    func findAll(sortedBy: String) -> T?
}