Inout parameter in async callback does not work as expected

Question

I\'m trying to insert functions with inout parameter to append data received from async callback to an outside array. However, it does not work. And I tried eve

Answer 1

I had a similar goal and ran into the same issue where results inside the closure were not being assigned to my global inout variables. @rintaro did a great job of explaining why this is the case in a previous answer.

I am going to include here a generalized example of how I worked around this. In my case I had several global arrays that I wanted to assign to within a closure, and then do something each time (without duplicating a bunch of code).

// global arrays that we want to assign to asynchronously
var array1 = [String]()
var array2 = [String]()
var array3 = [String]()

// kick everything off
loadAsyncContent()

func loadAsyncContent() {

    // function to handle the query result strings
    // note that outputArray is an inout parameter that will be a reference to one of our global arrays
    func resultsCallbackHandler(results: [String], inout outputArray: [String]) {

        // assign the results to the specified array
        outputArray = results

        // trigger some action every time a query returns it's strings
        reloadMyView() 
    }

    // kick off each query by telling it which database table to query and
    // we're also giving each call a function to run along with a reference to which array the results should be assigned to
    queryTable("Table1") {(results: [String]) -> Void in resultsCallbackHandler(results, outputArray: &self.array1)}
    queryTable("Table2") {(results: [String]) -> Void in resultsCallbackHandler(results, outputArray: &self.array2)}
    queryTable("Table3") {(results: [String]) -> Void in resultsCallbackHandler(results, outputArray: &self.array3)}
}

func queryTable(tableName: String, callback: (foundStrings: [String]) -> Void) {

    let query = Query(tableName: tableName)
    query.findStringsInBackground({ (results: [String]) -> Void in

        callback(results: results)
    })
}

// this will get called each time one of the global arrays have been updated with new results
func reloadMyView() {

    // do something with array1, array2, array3
}