data-as-struct.swift

//
//  main.swift
//  Test
//
//  Created by Chris Eidhof on 29/08/15.
//  Copyright © 2015 Chris Eidhof. All rights reserved.
//

import Foundation
import Quartz

final class Box<A> {
    let unbox: A
    init(_ value: A) { unbox = value }
}


struct Data {
    private var boxedData: Box<NSMutableData>
    var data: NSData { return boxedData.unbox }
    init(data: NSData = NSData()) {
        self.boxedData = Box(NSMutableData(data: data))
    }
}

/// Immutable

extension Data {
    var length: Int { return data.length }
    var bytes: UnsafePointer<Void> {
        return data.bytes
    }
}

/// Mutating

extension Data {
    private var mutableData: NSMutableData {
        mutating get {
            if !isUniquelyReferencedNonObjC(&boxedData) {
                boxedData = Box(NSMutableData(data: data))
            }
            return boxedData.unbox
        }
    }
    
    mutating func append(other: NSData) {
        mutableData.appendData(other)
    }
}

var data = Data(data: NSData())
data.append(NSData())
print(data.data)