Converting an array containing structure to json - arrays

Question

I'm trying to convert an array into json but can't get it to work. It says the array is an invalid type to convert to json, but it's just an array of ints.
//These are for me to able to use time
let date = NSDate()
let calendar = NSCalendar.current
//This is the structure that my array will be filled with
struct Day
{
var week: Int?
var date: Int?
var month: Int?
var year: Int?
var weekday: Int?
}
//This is my array
var theArrayContainingAllTheUserData = [Day]()
var numberofloops = 0
//This is a loop that fills my array with data
while theArrayContainingAllTheUserData.count < 20
{
var theincreasingnumberofdays: NSDate {
return NSCalendar.current.date(byAdding: .day, value: numberofloops, to: NSDate() as Date)! as NSDate
}
let myCalendar = NSCalendar(calendarIdentifier: NSCalendar.Identifier.gregorian)!
numberofloops=numberofloops+1
var ScoopDay = Day()
ScoopDay.week=Int(myCalendar.component(.weekOfYear, from: theincreasingnumberofdays as Date!))
ScoopDay.date=Int(myCalendar.component(.day, from: theincreasingnumberofdays as Date!))
ScoopDay.month=Int(myCalendar.component(.month, from: theincreasingnumberofdays as Date!))
ScoopDay.year=Int(myCalendar.component(.year, from: theincreasingnumberofdays as Date!))
ScoopDay.weekday=Int(myCalendar.component(.weekday, from: theincreasingnumberofdays as Date!))
theArrayContainingAllTheUserData.append(ScoopDay)
}
//And here is my failed attempt at converting it to json
do {
let jsonData = try JSONSerialization.data(withJSONObject: theArrayContainingAllTheUserData, options: JSONSerialization.WritingOptions.prettyPrinted)
} catch {
print(error.localizedDescription)
}
Getting Error:
2016-10-28 13:20:09.669 jsona arrayen[3284:332873] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Invalid type in JSON write (_SwiftValue)'
First throw call stack:
(
0 CoreFoundation 0x000000010840834b __exceptionPreprocess + 171
1 libobjc.A.dylib 0x0000000107e6921e objc_exception_throw + 48
2 CoreFoundation 0x0000000108471265 +[NSException raise:format:] + 197
3 Foundation 0x000000010795d284 _writeJSONValue + 668
4 Foundation 0x000000010795d6d9 ___writeJSONArray_block_invoke + 132
5 CoreFoundation 0x00000001083ae36f __NSArrayEnumerate + 607
6 Foundation 0x000000010795d3df _writeJSONArray + 330
7 Foundation 0x000000010795d204 _writeJSONValue + 540
8 Foundation 0x000000010795cf94 -[_NSJSONWriter dataWithRootObject:options:error:] + 124
9 Foundation 0x000000010795ce74 +[NSJSONSerialization dataWithJSONObject:options:error:] + 333
10 ??? 0x0000000116ddd3cb 0x0 + 4678603723
11 jsona arrayen 0x0000000107892620 main + 0
12 CoreFoundation 0x00000001083ad25c __CFRUNLOOP_IS_CALLING_OUT_TO_A_BLOCK__ + 12
13 CoreFoundation 0x0000000108392304 __CFRunLoopDoBlocks + 356
14 CoreFoundation 0x0000000108391a75 __CFRunLoopRun + 901
15 CoreFoundation 0x0000000108391494 CFRunLoopRunSpecific + 420
16 GraphicsServices 0x000000010d796a6f GSEventRunModal + 161
17 UIKit 0x0000000108f3bf34 UIApplicationMain + 159
18 jsona arrayen 0x00000001078926e9 main + 201
19 libdyld.dylib 0x000000010b8e968d start + 1
20 ??? 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException