JSONSerialization Invalid type in JSON write (_SwiftValue)

Question

Why does the following code give me the error:

Invalid type in JSON write (_SwiftValue).

The error is thrown on this line:

Answer 1

I was getting this runtime error because my dictionary was like this:

var dictionary: [AnyHashable: Any] = [:]
let elapsedTime = Date.timeIntervalSince(oldDate)
dictionary["elapsedTime"] = elapsedTime

Can you tell me what the problem is? _{^{hover your mouse on the box below to see answer!}}

elapsedTime's type is Function it's not TimeInterval. I needed to change Date. to Date(). ie use the instance method rather than the static method. When you're dictionary values are Any then this sort of issue doesn't get found until a runtime error where it can't serialize the dictionary to a JSON string...