DispatchToData-Swift3.swift

import Foundation

#if os(macOS) || os(iOS) || os(tvOS) || os(watchOS)

    extension Data {

        init(referencing data: DispatchData) {
            self = (data as AnyObject) as! Data
        }

    }

    extension DispatchData {

        init(referencing data: Data) {
            guard !data.isEmpty else {
                self = .empty
                return
            }

            // will perform a copy if needed
            let nsData = data as NSData

            if let dispatchData = ((nsData as AnyObject) as? DispatchData) {
                self = dispatchData
            } else {
                self = .empty
                nsData.enumerateBytes { (bytes, byteRange, _) in
                    let innerData = Unmanaged.passRetained(nsData)
                    let buffer = UnsafeBufferPointer(start: bytes.assumingMemoryBound(to: UInt8.self), count: byteRange.length)
                    let chunk = DispatchData(bytesNoCopy: buffer, deallocator: .custom(nil, innerData.release))
                    append(chunk)
                }
            }
        }

    }

#endif

let nsData1 = "Hello, ".data(using: .utf8)! // => 7 bytes
let nsData2 = "world!".data(using: .utf8)! // => 6 bytes

var dData = DispatchData(referencing: nsData1) // => DispatchData
let dData2 = DispatchData(referencing: nsData2) // => DispatchData
dData.append(dData2)

dData.count // => 13

var numberOfChunks = 0
dData.enumerateBytes { _ in numberOfChunks += 1 }
numberOfChunks // => 2

let combinedNsData = Data(referencing: dData) // => 13 bytes
type(of: combinedNsData as NSData) // OS_dispatch_data.Type