Swift：现在应该将NSError视为旧版吗？ [英] Swift: Should NSError now be considered as legacy?

问题描述

文档和流行博客建议使用do-catch完成Swift错误处理并处理ErrorType枚举或NSError实例。

The docs and popular blogs suggest Swift error handling be done with do-catch and to handle an ErrorType enum or an NSError instance.

ErrorType枚举和NSError实例是在尝试捕获块中互斥？如果没有，那么如何实现同时抛出两者的函数呢？

Are ErrorType enum and NSError instances mutually exclusive in a try catch block? If not, how do you implement a function that throws both?

我已经将NSError实例与这样的枚举相关联，这似乎可以正常工作，但这是否是de返回详细的错误信息的事实方法？

I have associated an NSError instance to an enum like so, which seems to work, but is this the de facto way of returning detailed error information?

enum Length : ErrorType {
    case NotLongEnough(NSError)
    case TooLong(NSError)
}

func myFunction() throws {
    throw Length.NotLongEnough(NSError(domain: "domain", code: 0, userInfo: [NSLocalizedFailureReasonErrorKey: "Not long enough mate"]))
}

do {
    try myFunction()
} catch Length.NotLongEnough(let error) {
    print("\(error)")
}

此示例显示ErrorType如何

This example shows how ErrorType can be cast to NSError.

do {
    let str = try NSString(contentsOfFile: "Foo.bar",
                           encoding: NSUTF8StringEncoding)
}
catch let error as NSError {
    print(error.localizedDescription)
}

我找不到符合NSString的ErrorType的错误枚举，所以我们应该假设它是NSError实例？当然可以确保可以运行代码，但是文档一定会让我们知道。 （不胜感激，我可能会误读文档）

I can't find an error enum that conforms to ErrorType for NSString so should we assume it will be an NSError instance ? Granted we could run the code to be sure, but surely the docs should let us know. (I appreciate I might have mis-read the docs)

推荐答案

NSError 类采用 ErrorType 接口，任何与 ErrorType 兼容的类都可以强制转换为 NSError 。在在文档中。

NSError class adopts ErrorType interface and any ErrorType-conformant class can be casted to NSError. These features are described here in the docs.

您可以放心地坚持 ErrorType

enum CommonError: ErrorType {
    case InternalInconsistency(String)
}

func boom() throws {
    throw CommonError.InternalInconsistency("Boom!")
}

do {
    try boom()
} catch {
    print(error) // InternalInconsistency("Boom!")
    print(error as NSError) // Error Domain=CommonError Code=0 "(null)"
}

do {
    try boom()
} catch let CommonError.InternalInconsistency(msg) {
    print("Error: \(msg)") // Error: Boom!
}

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