Swift protocol extension: fatal error: can't unsafeBitCast between types of different sizes

Question

我定义了一个带有协议扩展的协议来简化 NSError 的使用。

protocol NSErrorConvertible: RawRepresentable {
    var domain: String { get }
    var localizedDescription: String { get }
}

extension NSErrorConvertible where RawValue == Int {
    func generateError(parameters parameters: [String] = []) -> NSError {
        let error = self.generateError(format: self.localizedDescription, parameters: parameters)
        return error
    }

    func generateError(format format: String, parameters: [String] = []) -> NSError {
        let description = String(format: format, arguments: parameters) // <-- BREAK
        let error = NSError(domain: self.domain, code: self.rawValue, localizedDescription: description)
        return error
    }
}

extension NSError {
    convenience init(domain: String, code: Int, localizedDescription: String) {
        let userInfo = [NSLocalizedDescriptionKey : localizedDescription]
        self.init(domain: domain, code: code, userInfo: userInfo)
    }
}

协议的使用方式如下：

enum DefaultEngineErrors: Int, NSErrorConvertible {
    case ImagesNotSupported
    case FooDoesNotHaveABar
    case NilBar

    var domain: String { return "DefaultEngineErrors" }

    var localizedDescription: String {
        switch self {
        case .ImagesNotSupported: return "%s: Images are not supported."
        case .FooDoesNotHaveABar: return "%s: Foo does not have a bar."
        case .NilBar:             return "%s: The bar is nil."
        }
    }
}

下面是协议扩展方法的调用方式：

let error = DefaultEngineErrors.FooDoesNotHaveABar.generateError(parameters: ["\(foo.id)"])

当此代码为运行时，调试器在第二个 generateError 扩展函数中构建描述的行中断，调试器控制台中显示以下消息：

致命错误：无法在不同大小的类型之间进行 unsafeBitCast

请注意，如果我将对 String(format:) 的调用替换为 format，一切正常。

问：我在这里做的有什么问题吗？

除此之外，我无法检查协议扩展中的参数。当我尝试时显示以下消息：

(lldb) po format
error: <EXPR>:1:1: error: non-nominal type '$__lldb_context' (aka 'Self') cannot be extended
extension $__lldb_context {                            
^         ~~~~~~~~~~~~~~~
<EXPR>:15:5: error: value of type 'DefaultEngineErrors' has no member '$__lldb_wrapped_expr_54'
    $__lldb_injected_self.$__lldb_wrapped_expr_54(     
    ^~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~

Answer 1

Swift string Array is not compatible with CVarArgType... or [CVarArgType]

尝试使用。

extension NSErrorConvertible where RawValue == Int {
    func generateError(format format: String) -> NSError {
        let error = NSError(domain: self.domain, code: self.rawValue, localizedDescription: format)
        return error
    }
    func generateError(args : CVarArgType...) -> NSError {
        let returnString = NSString(format: self.localizedDescription, arguments: getVaList(args)) as String
//        let returnString = withVaList(args) {
//            NSString(format: self.localizedDescription, arguments: [=10=])
//        } as String
        let error = generateError(format: returnString)
        return error
    }
}

enum DefaultEngineErrors: Int, NSErrorConvertible {
    case ImagesNotSupported
    case FooDoesNotHaveABar
    case FooWithMultiPar
    case NilBar

    var domain: String { return "DefaultEngineErrors" }

    var localizedDescription: String {
        switch self {
        case .ImagesNotSupported: return "%@: Images are not supported."
        case .FooDoesNotHaveABar: return "%@: Foo does not have a bar."
        case .FooWithMultiPar: return "%@:%@ Foo does not have a bar."
        case .NilBar:             return "%@: The bar is nil."
        }
    }
}

print(DefaultEngineErrors.FooDoesNotHaveABar.generateError("test"))
print(DefaultEngineErrors.FooWithMultiPar.generateError("test1","test2"))

勾选

Swift protocol extension: fatal error: can't unsafeBitCast between types of different sizes

Swift protocol extension: fatal error: can't unsafeBitCast between types of different sizes

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