Dan Rosenstark, author of MIDI Designer, on Tech & Music

Dan Rosenstark

Dan Rosenstark, Author & CEO of MIDI Designer, muses about all things tech. Particularly: Notes on software development in Swift, Objective-C, and many non-Apple languages. Also: lots of random technology notes on OS X and iOS.

Showing all posts tagged "Swift"

Breakpoint Swift Deinit in Xcode

Setting up the Breakpoint
It's actually very simple to breakpoint the deinit method of a Swift class. Given a class called Test47, the symbolic breakpoint merely looks like this:

And that's about it.

  1. If there is no body to your deinit method, the breakpoint will not fire (it gets optimized out or something similar).
  2. There is no difference in syntax, for the Xcode symbolic breakpoints, between class and instance methods.
  3. There are no deinit methods for structs, so your SOL on that one.

Lazy Array in Swift

Obviously if you google "lazy array in Swift," you'll find out the right way to do this, which uses NSPointerArray and whatever else. As you should.

But sometimes you want to make your own to see how far you can get in half an hour with generics. Here's my naive implementation.

import Foundation

private class WeakWrapperAnyObject> {
weak var thing: T?
init(_ thing:T) {
self.thing = thing

struct WeakArrayAnyObject> : Sequence {
private var array: [WeakWrapper<T>] = []
var count: Int { return objects.count }
init(_ objects: [T]) {
var objects: [T] {
get {
let retVal: [T?] = array.map { $0.thing != nil ? $0.thing : nil }
return retVal.flatMap { $0 }
mutating func append(_ object: T) {
mutating func append(_ objects: [T]) {
array.append(contentsOf: objects.map { WeakWrapper($0) })
mutating func compress() {
array = array.filter{ $0.thing != nil }
// MARK: - Sequence Protocol methods
typealias Iterator = IndexingIterator<Array<T>>
func makeIterator() -> Iterator {
return objects.makeIterator()

let firstObject = NSString(string: "one")
var things = WeakArray([firstObject, NSString(string: "two"), NSString(string: "three")])
for thing in things {
print("Just one \(thing)")

Of course, I did have to look some stuff up, particularly to understand how easy Sequence was to implement (since I already have an array).