Swift 5.0：'withUnsafeBytes'已被弃用：使用`withUnsafeBytes （......）

Question

我之前在Swift 4.2中使用此代码生成一个id：

public static func generateId() throws -> UInt32 {
    let data: Data = try random(bytes: 4)
    let value: UInt32 = data.withUnsafeBytes { $0.pointee } // deprecated warning!
    return value // + some other stuff 
}

withUnsafeBytes在Swift 5.0上弃用。我怎么解决这个问题？

Answer 1

在Swift 5中，withUnsafeBytes()的Data方法用（无类型的）UnsafeRawBufferPointer调用闭包，你可以从原始记忆中获取load()值：

let value = data.withUnsafeBytes { $0.load(as: UInt32.self) }

（比较Swift论坛中的How to use Data.withUnsafeBytes in a well-defined manner?）。请注意，这要求内存在4字节边界上对齐。有关替代方案，请参阅round trip Swift number types to/from Data。

另请注意，从Swift 4.2开始，您可以使用新的Random API创建一个随机的32位整数：

let randomId = UInt32.random(in: .min ... .max)

Answer 2

在Xcode 10.2上，使用$0.load(as:)的Swift 5在从指针读取或写入时都不适用于我。

相反，使用$0.baseAddress?.assumingMemoryBound(to:)似乎运作良好。

从指针缓冲区读取示例（代码与问题无关）：

var reachability: SCNetworkReachability?
data.withUnsafeBytes { ptr in
    guard let bytes = ptr.baseAddress?.assumingMemoryBound(to: Int8.self) else {
        return
    }
    reachability = SCNetworkReachabilityCreateWithName(nil, bytes)
}

写入缓冲区指针的示例（代码与问题无关）：

try outputData.withUnsafeMutableBytes { (outputBytes: UnsafeMutableRawBufferPointer) in
    let status = CCKeyDerivationPBKDF(CCPBKDFAlgorithm(kCCPBKDF2),
                                      passphrase,
                                      passphrase.utf8.count,
                                      salt,
                                      salt.utf8.count,
                                      CCPseudoRandomAlgorithm(kCCPRFHmacAlgSHA1),
                                      rounds,
                                      outputBytes.baseAddress?.assumingMemoryBound(to: UInt8.self),
                                              kCCKeySizeAES256)
    guard status == kCCSuccess else {
        throw Error.keyDerivationError
    }
}

问题的代码如下：

let value = data.withUnsafeBytes { 
    $0.baseAddress?.assumingMemoryBound(to: UInt32.self)
}

在'withUnsafeBytes' is deprecated: use withUnsafeBytes<R>(…)警告持续存在的情况下，它看起来像the compiler can get confused when the closure has only one line。使闭包有两行或更多行可能会消除歧义。