Swift 3 - sending the pointer of an optionally bound variable - iOS

Question

I am currently converting my swift files to swift 3 and there is a runtime exception that involves pointers. Here is the code:

var sectionChanges:NSArray? = nil
var rowChanges:NSArray? = nil

databaseView.getSectionChanges(&sectionChanges!, rowChanges: &rowChanges!, for: notifications, with: mappings)

fatal error: unexpectedly found nil while unwrapping an Optional value

function signature specialization ) -> () to @callee_owned (@unowned Swift.UnsafeBufferPointer) -> (@out ()), Argument Types : [@callee_owned (@unowned Swift.UnsafeBufferPointer) -> ()]> of generic specialization of Swift.StaticString.withUTF8Buffer ((Swift.UnsafeBufferPointer) -> A) -> A

EDIT: Definition of getSectionChanges():

open func getSectionChanges(_ sectionChangesPtr: AutoreleasingUnsafeMutablePointer<NSArray>?, rowChanges rowChangesPtr: AutoreleasingUnsafeMutablePointer<NSArray>?, for notifications: [NSNotification], with mappings: YapDatabaseViewMappings)

Please help?!

Can you rewrite your `getSectionChanges` so it would just return tuple with changes arrays, instead of using `inout` parameters? Trust me, it will save you a lot of time and efforts in future. — user28434'mstep, Oct 18 '16 at 12:22
Where does `getSectionChanges()` come from and how is it defined? — Martin R, Oct 18 '16 at 12:23
@user28434 that's a great suggestion, slipped my mind. But is there no way I can send a pointer of an optional variable?! GAH I hate these upgrades. — Koushik Ravikumar, Oct 18 '16 at 12:23
@MartinR, edited the question to include the function definition. — Koushik Ravikumar, Oct 18 '16 at 12:26
@KoushikKumar, for the edit with definition of `getSectionChanges`: change `AutoreleasingUnsafeMutablePointer?` to `inout NSArray?`. And in future it's better to use swift's array with properly defined content type. — user28434'mstep, Oct 18 '16 at 12:27
@user28434, I am using the YapDatabase Framework and the function is defined within the framework. I'm afraid I cannot edit the definition. — Koushik Ravikumar, Oct 18 '16 at 12:31
Well then, you may try using non-optional type with default empty array value, hm. — user28434'mstep, Oct 18 '16 at 12:36
@user28434, that seemed to work! Thanks! I just hope it is stable. — Koushik Ravikumar, Oct 19 '16 at 09:30

score 0 · Answer 1 · answered Oct 19 '16 at 10:32

0

As the method definition implying: parameter AutoreleasingUnsafeMutablePointer? won't accept address of nil NSArray object. So you should use the following code to call the method:

var sectionChanges = NSArray()
var rowChanges = NSArray()

databaseView.getSectionChanges(&sectionChanges, rowChanges: &rowChanges, for: notifications, with: mappings)

answered Oct 19 '16 at 10:32

Zhou Jason

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The thing is, sectionChanges and rowChanges have a possibility of being assigned a nil object. – Koushik Ravikumar Oct 19 '16 at 11:37

score 0 · Accepted Answer · answered Oct 19 '16 at 11:40

Initialising the optional variable to something other than nil seems to have helped. Answering this question myself, in case it could be useful to somebody else.

var sectionChanges:NSArray? = NSArray()
var rowChanges:NSArray? = NSArray()

databaseView.getSectionChanges(&(sectionChanges)!, rowChanges: &(rowChanges)!, for: notifications, with: mappings)

Swift 3 - sending the pointer of an optionally bound variable - iOS

2 Answers2