Runtime Error When Using Corefoundation Objects in a Swift Nsobject Subclass

Swift 2.0 Set not working as expected when containing NSObject subclass

I played with your code a bit. I was able to get it working by no longer subclassing NSObject, but instead conforming to the Hashable protocol:

class A: Hashable {
    let h: Int

    init(h: Int) {
        self.h = h
    }

    var hashValue: Int {
        return h
    }

}

func ==(lhs: A, rhs: A) -> Bool {
    return lhs.hashValue == rhs.hashValue
}

let a = A(h: 1)
let b = A(h: 1)

var sa = Set([a])
let sb = Set([b])

sa.subtract(sb).count // Swift1.2 prints 0, Swift 2 prints 1

sa.contains(a) // Swift1.2 true, Swift 2 true
sa.contains(b) // Swift1.2 true, Swift 2 false

a.hashValue == b.hashValue

When you were inheriting from NSObject, your == overload wasn't actually being executed. If you want this to work with NSObject, you'd have to override isEquals:

override func isEqual(object: AnyObject?) -> Bool {
    if let object = object as? A {
        return object.h == self.h
    } else  {
        return false
    }
}

Swift native base class or NSObject

Swift classes that are subclasses of NSObject:

are Objective-C classes themselves
use objc_msgSend() for calls to (most of) their methods
provide Objective-C runtime metadata for (most of) their method implementations

Swift classes that are not subclasses of NSObject:

are Objective-C classes, but implement only a handful of methods for NSObject compatibility
do not use objc_msgSend() for calls to their methods (by default)
do not provide Objective-C runtime metadata for their method implementations (by default)

Subclassing NSObject in Swift gets you Objective-C runtime flexibility but also Objective-C performance. Avoiding NSObject can improve performance if you don't need Objective-C's flexibility.

Edit:

With Xcode 6 beta 6, the dynamic attribute appears. This allows us to instruct Swift that a method should use dynamic dispatch, and will therefore support interception.

public dynamic func foobar() -> AnyObject {
}

Why does object become NSZombie only when inherit from NSObject?

tl;dr: because NSZombies are implemented to only affect NSObject and its subclasses. (This doesn't have to do with Swift, either: Obj-C objects which aren't subclasses of NSObject also won't become zombies.)

Upon initialization (__CFInitialize, called when the framework is loaded), the CoreFoundation framework sets up a lot low-level Foundation and CoreFoundation behaviors; among other things, it looks for the NSZombieEnabled environment variable, and if present, enables zombies by calling the __CFZombifyNSObject function:

; Disassembly from Hopper on /System/Library/Frameworks/CoreFoundation.framework/CoreFoundation on macOS Catalina
0000000000001cc0         lea        rdi, qword [aNszombieenable]                ; argument #1 for method ___CFgetenv, "NSZombieEnabled"
0000000000001cc7         call       ___CFgetenv                                 ; ___CFgetenv
0000000000001ccc         test       rax, rax
0000000000001ccf         je         loc_1cee

0000000000001cd1         mov        al, byte [rax]                              ; DATA XREF=sub_1bb8ec
0000000000001cd3         or         al, 0x20
0000000000001cd5         cmp        al, 0x79
0000000000001cd7         jne        loc_1cee

0000000000001cd9         cmp        byte [___CFZombieEnabled], 0x0              ; ___CFZombieEnabled
0000000000001ce0         jne        loc_1cee

0000000000001ce2         mov        byte [___CFZombieEnabled], 0xff             ; ___CFZombieEnabled
0000000000001ce9         call       ___CFZombifyNSObject                        ; ___CFZombifyNSObject

When zombies are enabled, __CFZombifyNSObject replaces the implementation of -[NSObject dealloc] with a different implementation (__dealloc_zombie):

// Hopper-generated pseudo-code:
void ___CFZombifyNSObject() {
    rax = objc_lookUpClass("NSObject");
    method_exchangeImplementations(class_getInstanceMethod(rax, @selector(dealloc)), class_getInstanceMethod(rax, @selector(__dealloc_zombie)));
    return;
}

This means that all subclasses of NSObject and their descendants, upon deallocation, will call through to __dealloc_zombie. So what does __dealloc_zombie do?

// Hopper-generated pseudo-code:
/* @class NSObject */
-(void)__dealloc_zombie {
    rbx = self;
    if ((rbx & 0x1) != 0x0) goto loc_175ed5;

loc_175e3f:
    if (*(int8_t *)___CFZombieEnabled == 0x0) goto loc_175eee;

loc_175e4c:
    rax = object_getClass(rbx);
    var_20 = 0x0;
    rax = asprintf(&var_20, "_NSZombie_%s", class_getName(rax));
    rax = objc_lookUpClass(var_20);
    r14 = rax;
    if (rax == 0x0) {
            r14 = objc_duplicateClass(objc_lookUpClass("_NSZombie_"), var_20, 0x0);
    }
    free(var_20);
    objc_destructInstance(rbx);
    object_setClass(rbx, r14);
    if (*(int8_t *)___CFDeallocateZombies != 0x0) {
            free(rbx);
    }
    goto loc_175ed5;

loc_175ed5:
    if (**___stack_chk_guard != **___stack_chk_guard) {
            __stack_chk_fail();
    }
    return;

loc_175eee:
    if (**___stack_chk_guard == **___stack_chk_guard) {
            _objc_rootDealloc(rbx);
    }
    else {
            __stack_chk_fail();
    }
    return;
}

In more human-readable terms, it:

Looks up [self class]
If there isn't already a class named _NSZombie_<our class name>, it creates one by duplicating the _NSZombie_ class and gives the duplicate a new name (this creates a copy of the class with all of its method implementations, or lack thereof)
It tears down self, and replaces its class with the new class, so that if you message it in the future, you dispatch to _NSZombie_<whatever>

_NSZombie_ is a class which implements no methods, so sending it any message (method call) ends up falling into a code path in message forwarding which prints out the "message sent to deallocated instance" message.

Effectively, this method of implementing zombies hinges on inheritance from NSObject (because all NSObject subclasses should call [super dealloc] on deallocation, eventually reaching [NSObject dealloc]); things which don't inherit from NSObject don't inherit this implementation. (You can also actually see this by implementing an NSObject subclass which doesn't call [super dealloc] in its -dealloc implementation — the object won't get zombified on release.)

Do NSZombies have to be implemented this way? No, it's certainly possible to imagine other schemes which would allow pure Swift objects to participate (Swift runtime initialization could also look up the NSZombieEnabled environment variable and do something similar), but there's somewhat less of a benefit to putting in the effort. As Rob mentions in his answer, this works largely because we're able to swizzle out the class of the deallocated instance (this is actually possible with the Swift runtime, but not exposed externally), but crucially, even if we did this, it wouldn't help cases of static method dispatch, which is possible on object types in Swift (e.g. for final classes). [Alexander alludes to this in his comment.]

So, largely, it's really easy to implement this way for Obj-C, and there are somewhat limited benefits for taking the time to do this for pure Swift classes too.

Return an array created from custom objects in Swift where they aren't known until runtime?

You can use generics.

func fillAnObjectClassArrayGivenURL<T: AnyObject>(urlString: String, className: T.Type) -> [T]

Why is executeFetchRequest not returning subclass objects when run under XCTest using Swift?

I had a similar question. Making my entity class public solves the issue and I get the right class type.(CoreData class miss match in unit test)

Can I avoid subclassing NSObject to repetitively call a method?

Your code does not cause a stack overflow, because dispatch_after() only
dispatches the block for later execution and then returns.

A possible disadvantage of your solution is that it starts a new timer every
60 seconds. Timers are not 100% precise, so small differences could accumulate.

A better solution (if you want to avoid NSTimer) would be to use a dispatch
timer, as described in this answer
to Do something every x minutes in Swift.