[SR-4950] Swift does not honor NSMutableArray generics from objective-c classes

[swift-ci]

Previous ID	SR-4950
Radar	None
Original Reporter	tourultimate (JIRA User)
Type	Bug

Attachment: Download

Environment

xcode 8.2.1

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 1 | |Component/s | Compiler | |Labels | Bug, ClangImporter | |Assignee | None | |Priority | Medium | md5: 3c3968f70787ac6cfb10e89bbcfe9e20

Issue Description:

Consider the following objective-c classes:

```objective-c
@interface Layer : NSObject
@property (nonatomic, strong) NSString *name;
@end

@interface Map : NSObject

@property (nonatomic, strong, readonly) NSMutableArray\<Layer *> *layers;

@end
```

Trying to use them with swift like so:

```swift
let map = Map()

for layer in map.layers{
print(layer.name)
}
```

You will end up with compiler errors as the array is emitting AnyObjects instead of the expected type (Layer in this case)

[belkadan]

Yep, we're not able to import NSArray with generics right now, and that extends to NSMutableArray for consistency. I agree that it can be frustrating in cases like this, though.

[swift-ci]

Comment by tourultimate (JIRA)

Jordan,

I'm not quite sure what you mean that we aren't able to import NSArray with generics. If I change the code to this:

```
@property (nonatomic, strong, readonly) NSArray\<Layer *> *layers;
```

It works fine. It seems to be only a problem with NSMutableArray.

[belkadan]

That's imported as a Swift Array rather than a Foundation NSArray. We can't just do that for NSMutableArray because Swift arrays are value types, which means an update to the array isn't automatically visible across clients.

One workaround here is to expose your property as an NSArray, but declare the backing instance variable in the .m file to be an NSMutableArray.