At what point do we delete the object if the reference counter reaches zero?

As soon as the reference count of an object reaches zero, the Swift (or Objective-C) runtime immediately (i.e., in the same run loop) calls the deinit method of that object, after which the memory occupied by the object is released. If the object was created in an automatic release pool (autoreleasepool), then in Objective-C, the release will occur when exiting that pool (assuming the retain count is zero).

In Swift, Automatic Reference Counting (ARC) manages the lifecycle of objects, freeing memory immediately after there are no more strong references to the object.

class MyClass {
    deinit {
        print("Object MyClass released")
    }
}

var instance: MyClass? = MyClass() // Reference count = 1
instance = nil // Reference count = 0. deinit is called immediately.

@interface MyObject : NSObject
@end

@implementation MyObject

- (instancetype)init {
    self = [super init];
    if (self) {
        NSLog(@"Object MyObject created");
    }
    return self;
}

- (void)dealloc {
    NSLog(@"Object MyObject released");
    [super dealloc]; // Not required under ARC, but good practice for manual memory management (MRR)
}

@end

int main() {
    @autoreleasepool {
        MyObject *obj = [[MyObject alloc] init]; // retain count = 1
        // ... use obj ...
        // At the end of the autoreleasepool, if retain count <= 0, the object is released.
        // Under ARC, if obj becomes nil before exiting the pool, the release occurs immediately.
    }
    return 0;
}