Supplying NSMutableArray type to Objective C function in Swift

Question

I have a library function written in Objective C that has takes a pointer to a NSMutableArray. However, when I try to call it with a Swift array I get this error:

DiscoverViewController.swift:34:20: Could not find an overload for 'init' that
accepts the supplied arguments

However, if I pass nil, it works. That makes sense.

Here is an example of the Objective-C:

int ex:(NSMutableArray *)in { return in.count; }

And an example of the Swift:

ex([1,2,3,4]) // doesn't compile

ex(nil) // does compile

What do I have to do to convert/cast the Swift array to the NSMutableArray type that my library function is looking for?

Here is the full method signature in case my example is too simplified:

- (id) initWithTitle: (NSString *) title place: (PublicPlaceInfo *) place
datetimeInterval: (DateTimeInterval *) datetimeInterval costBracket: (int)
costBracket creatorId: (PersonID) creatorId cover: (Url) cover experienceId: 
(ExperienceID) experienceId numJoined: (int32_t) numJoined relatedJoined: 
(NSMutableArray *) relatedJoined;

And then I know it is failing at the relatedJoined section because I converted all other potentially anonymous instantiations to variables. I have to say, this is certainly not the most helpful compile error..

Tom van der Woerdt · Accepted Answer · 2014-06-03 18:44:56Z

6

ex([1,2,3,4]) // doesn't compile

This is because you're passing it a normal array, not a mutable array. Try converting it to a mutable array first: ex(NSMutableArray([1,2,3,4]))

ex(nil) // does compile

nil is a valid argument to NSMutableArray? which is why it works.

answered Jun 3, 2014 at 18:44

Tom van der Woerdt

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3 Comments

eatonphil Over a year ago

Ok so then I let the relatedJoined parameter equal to a var mutArr = [1,2,3,4] and it still does not compile. But according to the documentation, an array that is declared as "var" (not "let") is a mutable array.

Tom van der Woerdt Over a year ago

@phileaton: Swift's Array is not the same as NSArray. Docs reference Think of an Array in Swift to be a SWArray :-)

eatonphil Over a year ago

Haha alright, I guess I'm just disappointed there isn't native support since for conversion since NSArray and NSMutableArray are so fundamental in Objective-C.

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