Adding new element to Array - Swift 3 - core-data

Question

I have a Tableviewcontroller BeamsNameVC with 2 variables: Name and number.
If for example, the number is 7, and if I click on any row in this View controller, it will segue to another TableViewcontroller SpansListVC and than it will show 7 rows: S1, S2, S3, S4, S5, S6 & S7.
I want to save these Data, so I created 2 swift files:
class StructureElement: NSObject, NSCoding {
var name = ""
var nbrSpans = ""
var spans = [LoadDetailsForEachSpan]()
and
class LoadDetailsForEachSpan: NSObject, NSCoding {
var i_SpanName = ""
var i_Spanlength = ""
var i_ConcentratedLoadForEachSpans = [ConcentratedLoadForEachSpan]()
I created a protocol with the following:
let spanNbr = Int(structureElement[newRowIndex].nbrSpans)
let newElementDetailSpan = LoadDetailsForEachSpan()
for i in 0...spanNbr! {
newElementDetailSpan.i_SpanName = "S" + " \(i)"
structureElement[newRowIndex].spans.append(newElementDetailSpan)
}
If i run the application, it will segue to * SpansListVC* but all values are the last i.
Example:
if name is Test 7 and number of span is 7, I will be having inside *[Spans] * 7 values with the same name:
spans[0] = S 7
spans[1] = S 7
....
Any mistake with above code?

Answer 1

Welcome to the hell that mutable data objects can be ;). You are creating a single LoadDetailsForEachSpan instance and add that same instance a number of times to the array, while setting the i_SpanName property of that same instance every time the loop is iterated. You probably want to pull the instance creation into the loop:
for i in 0...spanNbr! {
let newElementDetailSpan = LoadDetailsForEachSpan()
newElementDetailSpan.i_SpanName = "S" + " \(i)"
structureElement[newRowIndex].spans.append(newElementDetailSpan)
}

Answer 2

Thanks #thm for your reply.
however, i find another solution as follow and it works:
var spanDetailAndLoadItem: [SpanDetailsAndLoads] = []
for var i in 1...nbr! {
let item = SpanDetailsAndLoads(name: "S\(i) - S\(i + 1)")
spanDetailAndLoadItem.append(item)
}
self.spans = spanDetailAndLoadItem