swift - 如何创建一个通用的完成闭包？

Question

我有以下协议(protocol):

protocol RESTAPIprotocol {
    associatedtype T: Object, Decodable
}

extension RESTAPIprotocol {

    func getList(sinceSyncToken: String = "",
                 pageLimit: Int = 100,
                 progress: Moya.ProgressBlock? = nil,
                 completion:@escaping (_ list: [T]?, _ error: AppError?) -> Void) { ... }

和对象:

final class RLMOrganization: RLMDefaults {
    typealias T = RLMOrganization
}

final class RLMProject: RLMDefaults {
    typealias T = RLMProject
}

final class RLMLocation: RLMDefaults {
    typealias T = RLMLocation
}

想像这样使用它:

class SyncEngine {

    let listCompletionClosure = { (_ list: [T]?, _ error: AppError?) -> Void in  ... }


    func syncOrganizations() {
        // Sync down from server and update our local DB.
        organizationsDAL.getList(sinceSyncToken: organizationsDAL.getLastSyncToken(), completion: listCompletionClosure)
    }

但是得到错误:

哪种方式有意义，但不明白我如何将用作 RESTAPIprotocol 一部分的泛型传递到泛型闭包中？

目标是尝试完成以下任务:

func syncOrganizations() {
    organizationsDAL.getList(sinceSyncToken: organizationsDAL.getLastSyncToken(), completion: listCompletionClosure)
}

func syncProjects() {
    projectsDAL.getList(sinceSyncToken: projectsDAL.getLastSyncToken(), completion: listCompletionClosure)
}

func syncLocations() {
    locationsDAL.getList(sinceSyncToken: locationsDAL.getLastSyncToken(), completion: listCompletionClosure)
}

Answer 1

把它改成"怎么样

let listCompletionClosure = { (_ list: [RLMOrganization]?, _ error: AppError?) -> Void in  ... }

完成句柄需要具体类型，并且您已在 RLMOrganization 类的上下文中定义了 T = RLMOrganization。

编辑:闭包不能是通用的，但函数可以:

func listCompletion<T: Decodable>(list: [T]?, error: AppError?) {
    // you must cast `list` to a  concrete type
}

func syncOrganizations() {
    organizationsDAL.getList(sinceSyncToken: organizationsDAL.getLastSyncToken(), completion: listCompletion)
}

func syncProjects() {
    projectsDAL.getList(sinceSyncToken: projectsDAL.getLastSyncToken(), completion: listCompletion)
}

func syncLocations() {
    locationsDAL.getList(sinceSyncToken: locationsDAL.getLastSyncToken(), completion: listCompletion)
}