CustomNSError協議做了什麼，我爲什麼要採用它？

Question

CustomNSError協議做什麼，爲什麼我應該採用它？
由蘋果公司提供的文件只規定：

Describes an error type that specifically provides a domain, code, and user-info dictionary.

我已經搜索在谷歌，但找不到與我的問題有什麼。

Answer 1

Every type that conforms to the Error protocol is implicitly bridged to NSError . This has been the case since Swift 2, where the compiler provides a domain (i.e., the mangled name of the type) and code (based on the discriminator of the enumeration type).

所以，你需要CustomNSError，LocalizedError和RecoverableError顯式運行映射NSError。

更多信息here。

實施例：

// Errors 

enum ServiceError: Int, Error, CustomNSError { 
    case unknownError = -1000 
    case serverReturnBadData 

    //MARK: - CustomNSError 

    static var errorDomain: String = "reverse.domain.service.error" 

    var errorCode: Int { return self.rawValue } 
    var errorUserInfo: [String : Any] { return [:] } //TODO: Return something meaningful here 
} 

extension NSError { 

    var serviceError: ServiceError? { 
     return (self.domain == ServiceError.errorDomain 
      ? ServiceError(rawValue: self.code) 
      : nil) 
    } 

    convenience init(serviceError: ServiceError) { 
     self.init(
      domain: ServiceError.errorDomain, 
      code: serviceError.rawValue, 
      userInfo: serviceError.errorUserInfo) 
    } 
}