Question

使用NSMutableData，我可以创建一个Int's或Float的数组，并将其存储到磁盘。

protocol BinaryConvertible
{
    init()
}

extension Int : BinaryConvertible {}


struct Storage<T: BinaryConvertible>
{
let data = NSMutableData()

func append(value: T)
{
    var input = value
    data.append(&input, length: sizeof(T))
}

func extract(index: Int) -> T
{
    var output = T()
    let range = NSRange(location: index * sizeof(T), length: sizeof(T))
    data.getBytes(&output, range: range)
    return output
}
}

Swift 3有一个新的Data类型，它使用了NSData。与String和NSString一样。我无法弄清楚如何添加例如Double使用新方法。

追加函数现在需要UnsafePointer<UInt8>，但是如何从Double或任何随机结构中创建这个？

Answer 1

使用指针是我在Swift中最不喜欢的事情之一，但它也提供了良好的学习体验。这对我有用：

struct Storage<T: BinaryConvertible>
{
    var data = Data()

    mutating func append(value: T)
    {
        var input = value
        let buffer = UnsafeBufferPointer(start: &input, count: 1)
        self.data.append(buffer)
    }

    func extract(index: Int) -> T
    {
        let startIndex = index * sizeof(T)
        let endIndex = startIndex + sizeof(T)

        var output = T()
        let buffer = UnsafeMutableBufferPointer(start: &output, count: 1)
        let _ = self.data.copyBytes(to: buffer, from: startIndex..<endIndex)

        return output
    }
}

var s = Storage<Double>()
s.append(value: M_PI)
s.append(value: 42)
s.append(value: 100)

print(s.extract(index: 0))
print(s.extract(index: 1))
print(s.extract(index: 2))

Answer 2

我喜欢使用+或+ =

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        this is second box
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样品

public protocol DataConvertible {
    static func + (lhs: Data, rhs: Self) -> Data
    static func += (lhs: inout Data, rhs: Self)
}

extension DataConvertible {
    public static func + (lhs: Data, rhs: Self) -> Data {
        var value = rhs
        let data = Data(buffer: UnsafeBufferPointer(start: &value, count: 1))
        return lhs + data
    }

    public static func += (lhs: inout Data, rhs: Self) {
        lhs = lhs + rhs
    }
}

extension UInt8 : DataConvertible { }
extension UInt16 : DataConvertible { }
extension UInt32 : DataConvertible { }

extension Int : DataConvertible { }
extension Float : DataConvertible { }
extension Double : DataConvertible { }

extension String : DataConvertible {
    public static func + (lhs: Data, rhs: String) -> Data {
        guard let data = rhs.data(using: .utf8) else { return lhs}
        return lhs + data
    }
}

extension Data : DataConvertible {
    public static func + (lhs: Data, rhs: Data) -> Data {
        var data = Data()
        data.append(lhs)
        data.append(rhs)

        return data
    }
}

如何将Int附加到新的Data结构（Swift 3）

2 个答案: