Question

我正在研究我的cloudkit方法的通用“结果”回调，但我不确定为什么无法解释“成功”回调。

参考：https://github.com/apple/swift-evolution/blob/master/proposals/0048-generic-typealias.md

import Foundation
import CloudKit

public enum CloudKitError: Error {
    case general(String)
}

public enum CloudKitResult<T, ResultError: Error> {
    case success(T)
    case failure(ResultError)
}

public typealias CloudKitFetchClosure<T> = (_ result: CloudKitResult<T, CloudKitError>) -> Void

public final class CloudKitController {

  public typealias T = CKRecord

      public func save(_ record: CKRecord, callback: CloudKitFetchClosure<T>) -> Void {

        self.publicDB.save(record, completionHandler: {updatedRecord, error in

            if let _: Error = error {

                DispatchQueue.main.async(execute: {
                    callback(.failure(.general("Something went wrong")))
                })

            } else {

                DispatchQueue.main.async(execute: {
                    callback(.success(updatedRecord))
                })
            }
        })
    }
}


member 'success' in 'CloudKitResult<T, CloudKitError>' (aka 'CloudKitResult<CKRecord, CloudKitError>') produces result of type 'CloudKitResult<T, ResultError>', but context expects 'CloudKitResult<T, CloudKitError>' (aka 'CloudKitResult<CKRecord, CloudKitError>')
                callback(.success(updatedRecord))

Answer 1

我必须从CloudKit解包返回的记录。编译器现在很高兴。

    public func save(_ record: CKRecord, callback: CloudKitFetchClosure<T>) -> Void {

    self.publicDB.save(record, completionHandler: {updatedRecord, error in

        if let _: Error = error {

            DispatchQueue.main.async(execute: {
                callback(.failure(.general("Something went wrong")))
            })

        } else {

            if let ckrecord: CKRecord = updatedRecord {

                DispatchQueue.main.async(execute: {
                    callback(.success(ckrecord))
                })
            }
        }
    })
}

评估通用表达式时Swift 3编译错误

1 个答案: