[swift-users] Decimal imported as NSDecimal not NSDecimalNumber in Swift 3 to Objective C

[Philippe Hausler]

NSDecimal is not toll free bridged, but it does have a bridge to NSDecimalNumber.

So take this for example:

@objc class Exam: NSObject {
        var grade: Double = 90.0
}

It would be reasonable to expect that is exposed in objc as:

@interface Exam : NSObject
@property double grade;
@end

and not:

@interface Exam : NSObject
@property NSNumber *grade;
@end

As it stands this is exposing as the structural type since that structural type comes from objective-c. Unlike String or Dictionary that have direct counterparts - NSDecimal and NSDecimalNumber both are sourced from the objective-c headers. That being said an API exposed in objc as returning a NSDecimalNumber should be exposed into swift as returning a Decimal (the struct NSDecimal). So if Exam was implemented in objc as such:

@interface Exam : NSObject
@property NSDecimalNumber *grade;
@end

that should be imported into swift as:

class Exam : NSObject {
	var grade : Decimal
}

> On Nov 11, 2016, at 2:58 PM, Adam C. Lickel via swift-users <swift-users at swift.org> wrote:
> 
> NSDecimal has toll-free bridging with NSDecimalNumber so you can still do as casting when talking to an Objective-C API.
> 
>> On Nov 11, 2016, at 2:56 PM, Chris Anderson via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>> 
>> Sure thing. Yeah, ideally the bridging would be fixed, but at the least, correcting the documentation will be a good start. Will file, thanks.
>> 
>> Best,
>> Chris Anderson
>> 
>>> On Nov 11, 2016, at 5:55 PM, Tony Parker <anthony.parker at apple.com <mailto:anthony.parker at apple.com>> wrote:
>>> 
>>> Hi Chris,
>>> 
>>> Can you file a radar or JIRA for us on this? It looks like something should be fixed in the documentation at least, or perhaps in the bridging.
>>> 
>>> - Tony
>>> 
>>>> On Nov 11, 2016, at 1:46 PM, Chris Anderson via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>>>> 
>>>> I'm having problems with the type conversion between a Swift `Decimal` and an Objective C `NSDecimalNumber`.
>>>> 
>>>> If I have the Swift class:
>>>> 
>>>>     @objc class Exam: NSObject {
>>>>         var grade: Decimal = 90.0
>>>>     }
>>>> 
>>>> And try to use that Swift class in Objective C, 
>>>> 
>>>>     Exam *exam = [[Exam alloc] init];
>>>>     NSDecimalNumber *result = [[NSDecimalNumber zero] decimalNumberByAdding:grade.value];
>>>> 
>>>> I get the error:
>>>> 
>>>> Sending 'NSDecimal' to parameter of incompatible type 'NSDecimalNumber * _Nonnull'
>>>> 
>>>> as it seems like `grade` is being treated as an `NSDecimal` not an `NSDecimalNumber`. This seems incorrect as per https://developer.apple.com/reference/foundation/nsdecimalnumber <https://developer.apple.com/reference/foundation/nsdecimalnumber> it says 
>>>> 
>>>> "The Swift overlay to the Foundation framework provides the Decimal structure, which bridges to the NSDecimalNumber class. The Decimal value type offers the same functionality as the NSDecimalNumber reference type, and the two can be used interchangeably in Swift code that interacts with Objective-C APIs. This behavior is similar to how Swift bridges standard string, numeric, and collection types to their corresponding Foundation classes."
>>>> 
>>>> So I'm not sure if 1) I'm doing something wrong. 2) there's an error in the documentation or 3) this is a Swift bug. Number 1 on that list is definitely the most likely, but I wanted to see what I’m missing here.
>>>> 
>>>> I don't want to explicitly make the values in my Swift class `NSDecimalNumber` because then I cannot do simple arithmetic operations such as `+` without doing the whole ugly `decimalNumberByAdding` dance.
>>>> 
>>>> Thanks for the help!
>>>> 
>>>> Best,
>>>> Chris Anderson
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>>> 
>> 
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