[swift-users] Storing ObjC NSDictionary as Swift [NSObject:AnyObject] leaks memory

[Jordan Rose]

Hi, jemmons. I managed to reproduce this in pure Swift code, and then changed it so that the Swift dictionary got released. In the latter version, no leaks were reported, so I think it's just a problem with our tools. (This isn't too surprising; the internals of a Swift Dictionary use some of the known-zero bits in the storage pointer to store flags, like "this dictionary came from Cocoa".)

I'ne filed a bug report with the Instruments team. Thanks for bringing this up!

Jordan


> On Jan 21, 2016, at 13:36 , Joshua Scott Emmons via swift-users <swift-users at swift.org> wrote:
> 
> Say you have something like the following (or just grab the attached project: https://dl.dropboxusercontent.com/u/364098/DictionaryLeak.zip <https://dl.dropboxusercontent.com/u/364098/DictionaryLeak.zip>)
> 
> 
> //SwiftModel.swift
> class SwiftModel : NSObject {
>   let prop: [NSObject:AnyObject]
>   init(dict: [NSObject:AnyObject]){
>     prop = dict
>   }
> }
> 
> //MyViewController.m
> - (void)viewDidLoad {
>   [super viewDidLoad];
> 
>   NSDictionary *dict = @{@"Thing" : @"Stuff"}; //Leaks!
>   SwiftModel *model = [[SwiftModel alloc] initWithDict:dict];
>   [self setSwiftModel: model];
> }
> 
> Running this in Instruments (Xcode 7.2 7C68) reports a leak:
> <Screen Shot 2016-01-21 at 3.27.47 PM.png>
> Is this actually leaking? Or is this just Instruments loosing track of what's actually holding on to the NSDictionary once it's bridged to swift-world?
> 
> Or am I completely overlooking some important concepts somewhere along the line? :) 
> 
> Cheers,
> -jemmons
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