如何将bytes属性从Objective-C转换到Swift?

Question

我有一个简单的Objective-C函数:

- (NSData *)xorData1:(NSData *)data1 data2:(NSData *)data2 resultLength:(NSInteger)length {
const char *data1Bytes = [data1 bytes]; // ??
const char *data2Bytes = [data2 bytes]; // ??
NSMutableData *xorData = [[NSMutableData alloc] init];
for (int i = 0; i < length; i++) {
const char xorByte = data1Bytes[i % data1.length] ^data2Bytes[i % data2.length];
[xorData appendBytes:&xorByte length:1];
}
return xorData;
}

我需要让它在Swift中工作。我该怎么做呢?

import CommonCrypto
func xor(firstData: Data, secondData: Data) -> Data {
let length = kCCKeySizeAES128
let firstDataBytes = firstData // ??
let secondDataBytes = secondData // ??
let xorData = NSMutableData()
for i in 0..<length {
var xorByte = firstDataBytes[i % firstData.count] ^ secondDataBytes[i % secondData.count];
xorData.append(&xorByte, length: 1)
}
return xorData as Data
}

Answer 1

你的Swift函数编译后，应该产生与Objective-C函数相同的结果。不需要bytes属性，因为Data是Collection，底层字节可以通过下标访问:

let d = Data([11, 22, 33, 44, 54])
print(d[2]) // 33

也不需要使用Cocoa类NSMutableData，使用SwiftData类型更简单:

func xor(firstData: Data, secondData: Data) -> Data {
let length = kCCKeySizeAES128
var xorData = Data()
for i in 0..<length {
let xorByte = firstData[i % firstData.count] ^ secondData[i % secondData.count];
xorData.append(xorByte)
}
return xorData
}

或者，使用map函数:

func xor(firstData: Data, secondData: Data) -> Data {
let length = kCCKeySizeAES128
return Data((0 ..< length).map {
firstData[$0 % firstData.count] ^ secondData[$0 % secondData.count]
})
}