Int工作时Int64不起作用

Question

I'm receiving a JSON and I want to parse it to get a value. I'm doing this

let ddd = oneJson["restaurantId"] as! Int
print("ddd = \(ddd)")
let restaurantId = oneJson["restaurantId"] as! Int64

as you see, I'm parsing the same field. Here's my JSON

"location":"location here location","restaurantId":0

The print statement works just fine, but I get an exception on oneJson["restaurantId"] as! Int64 oneJson["restaurantId"] as! Int64

Answer 1

I love this quirk in swift (NOT).

It's one of the least intuitive gotchas of the language I know of. So it turns out that when you get a Dictionary with type AnyObject, Ints, Doubles, Floats, ARE NOT stored as the Swift native types. They're stored as... surprise! NSNumber.

Which leads to a whole host of unintuitive behavior, for instance type checking AnyObjects to see whether you have a Double or an Int (it can't be done).

For the same reason, your code is failing. Change it to:

let ddd = oneJson["restaurantId"] as! Int
print("ddd = \(ddd)")
let restaurantId = (oneJson["restaurantId"] as? NSNumber)?.longLongValue

And remind yourself again and again that when it's an AnyObject you're casting from, Swift is hiding from you the fact that it does a cast from NSNumber to Swift base types, and that in truth, they're still just NSNumbers.

Answer 2

I would recommend, not to use Int64 (or Int32 ). Int will be working in most cases.

See this post about the different integers in Swift: https://stackoverflow.com/a/27440158/4687348

Answer 3

Yes, it's a known bug in Swift 3, which has been solved in Swift 4.
Now, you just write like this,

let n = NSNumber.init(value: 9223372036854775807) // 2^63 - 1
print(n, n as! Int64) // will print the right answer.