Swift 用do和catch替换防护罩

我有以下实现，我正在向ViewController提出问题以正确显示警报。正如您在我的代码中所看到的，我在一行中使用了guard let和try。我想这很管用，但不推荐

处理/重构代码以正确处理每个抛出案例的最佳方法是什么

enum ServiceError: Error {
  case ClassroomApplicationCreation(Error)
  case ClassroomDoesNotExist(Error)
  case ClassRoomSelectionError
}

func createClassroom() throws -> String {
    guard let selectedClass = try findClassroom() else {
      throw ServiceError.ClassSelectionError
    }
    guard let classURL = URL(string: selectedClass) else {
      throw ServiceError.ClassroomDoesNotExist
    }
    let authority = try Authority(url: classURL)
    let configuration = ClassroomApplicationConfig(className: selectedClass, redirectUri: nil, authority: authority)
    do {
      return try ClassRoom(configuration: configuration)
    } catch {
      throw ServiceError.ClassroomApplicationCreation(error)
    }
}

func findClassroom() throws -> String? {
    guard
      let selectedClass = UserDefaults.standard.string(forKey: selectedClass)
    else {
      throw ServiceError.ClassRoomSelectionError
    }
    do {
      return try serviceManager.retrieveClassroom(selectedClass)
    } catch {
      throw ServiceError.ClassRoomSelectionError
    }
}

假设

教室（配置：配置）

在失败时抛出

。classroomApplicationCreation

和

findClassroom

抛出

。classRoomSelectionError

并在成功时返回一个非可选的错误。代码可以减少为

enum ServiceError: Error {
   case classroomApplicationCreation(Error)
   case userDoesNotExist(Error) 
   case classRoomSelectionError
}

func createClassroom() throws -> ClassRoom {
    let selectedClass = try findClassroom()
    guard let classURL = URL(string: selectedClass) else {
       throw ServiceError.userDoesNotExist
    }
    let authority = try Authority(url: classURL)
    let configuration = ClassroomApplicationConfig(classId: selectedClass.ID, redirectUri: nil, authority: authority)
    return try ClassRoom(configuration: configuration)
}

假设

教室（配置：配置）

抛出

。classroomApplicationCreation

和

findClassroom

在失败时抛出

。classRoomSelectionError

，在成功时返回非可选的代码，代码可以减少为

enum ServiceError: Error {
   case classroomApplicationCreation(Error)
   case userDoesNotExist(Error) 
   case classRoomSelectionError
}

func createClassroom() throws -> ClassRoom {
    let selectedClass = try findClassroom()
    guard let classURL = URL(string: selectedClass) else {
       throw ServiceError.userDoesNotExist
    }
    let authority = try Authority(url: classURL)
    let configuration = ClassroomApplicationConfig(classId: selectedClass.ID, redirectUri: nil, authority: authority)
    return try ClassRoom(configuration: configuration)
}

---

返回类型应该是

教室

您可以重构，这样就没有任何防护或do/catch块：

func createClassroom() throws -> ClassRoom {
    let selectedClass = try findClassroom()
    let classURL = try makeClassURL(from: selectedClass)
    let authority = try Authority(url: classURL)
    let configuration = ClassroomApplicationConfig(classId: selectedClass.ID, redirectUri: nil, authority: authority)
    return try makeClassRoom(from: configuration)
}


func findClassroom() throws -> String {
    guard allIsWell else { throw ServiceError.ClassRoomSelectionError }
    return ""
}

func makeClassURL(from string: String) throws -> URL {
    guard let classURL = URL(string: string) else {
        throw ServiceError.UserDoesNotExist
    }
    return classURL
}

func makeClassRoom(from configuration: ClassroomApplicationConfig) throws -> ClassRoom {
    do {
        return try ClassRoom(configuration: configuration)
    } catch {
        throw ServiceError.ClassroomApplicationCreation(error)
    }
}

---

您可以重构，这样就没有任何防护或do/catch块：

func createClassroom() throws -> ClassRoom {
    let selectedClass = try findClassroom()
    let classURL = try makeClassURL(from: selectedClass)
    let authority = try Authority(url: classURL)
    let configuration = ClassroomApplicationConfig(classId: selectedClass.ID, redirectUri: nil, authority: authority)
    return try makeClassRoom(from: configuration)
}


func findClassroom() throws -> String {
    guard allIsWell else { throw ServiceError.ClassRoomSelectionError }
    return ""
}

func makeClassURL(from string: String) throws -> URL {
    guard let classURL = URL(string: string) else {
        throw ServiceError.UserDoesNotExist
    }
    return classURL
}

func makeClassRoom(from configuration: ClassroomApplicationConfig) throws -> ClassRoom {
    do {
        return try ClassRoom(configuration: configuration)
    } catch {
        throw ServiceError.ClassroomApplicationCreation(error)
    }
}

---

为什么可以沿着Authority init转发，而其他错误必须进行模糊处理？我想，如果你的方法抛出错误，你不应该在那里捕获错误。只需从findClassroom方法和课堂初始值设定项中抛出正确的错误。@LeoDabus，你能用一个例子详细说明一下吗？只需删除

do catch

，并从初始值设定项和findClassroom方法中抛出错误。你指的是最后一个

do catch

？你指的是哪一个初始值设定项？为什么可以沿着Authority init转发，而其他错误必须被混淆？如果你的方法抛出，你不应该在那里捕获错误。只需从findClassroom方法和课堂初始值设定项中抛出正确的错误。@LeoDabus，你能用一个例子详细说明一下吗？只需删除

do catch

，并从初始值设定项和findClassroom方法中抛出错误。你指的是最后一个

do catch

？您指的是哪个初始值设定项？我有固定的

findClassroom（）

method我有固定的

findClassroom（）

method