Swift 3评估通用表达式时出现编译错误

Question

我正在为我的cloudkit方法进行通用的“结果”回调，但我不确定为什么“成功”回调无法解释。

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

我不得不解开从CloudKit返回的记录。编译器现在很开心。

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)) 
       }) 
      } 
     } 
    }) 
}