JSON parsing float in swift4.1 has unexpected behaviour - swift

Question

A simple function that parse json variable and returns a float.
func parseMyFloat(jsonString: String) -> Float? {
if let data = jsonString.data(using: String.Encoding.utf8, allowLossyConversion: true),
let parsedJSON = try? JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions.allowFragments) as? [String : Any] {
if let parsedJSON = parsedJSON {
return parsedJSON["myFloat"] as? Float
}
}
return nil
}
Now if i try this.
print(parseMyFloat(jsonString: "{\"myFloat\":23.2322998046875}"))
// output: 23.2322998
output is fine but if I change 23.2322998046875 value to 23.2322998046 func returns nil.
print(parseMyFloat(jsonString: "{\"myFloat\":23.2322998}"))
// output: nil
Then I tried casting Any to Float which doesn't work.
let dic:[String : Any] = ["float1" : 23.2322998046875, "float2" : 23.2322998]
print(dic["float1"] as? Float) // prints nil
print(dic["float2"] as? Float) // prints nil
I have lots of float in my code, so after migrating to swift 4.1 I am having this issue.
Should I change all Float's to Double's ?? And 23.2322998046875 why works and why not 23.2322998??

Answer 1

If you want to keep your function as it is and don't want to modify the return value to Double, you can simply parse the JSON value as Double to avoid the issue of casting Any to Float as explained in the comments and then convert the Double to Float before returning it.
func parseMyFloat(jsonString: String) -> Float? {
if let data = jsonString.data(using: String.Encoding.utf8, allowLossyConversion: true), let parsedJSON = (try? JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions.allowFragments)) as? [String : Any], let myDouble = parsedJSON["myFloat"] as? Double {
return Float(myDouble)
}
return nil
}
parseMyFloat(jsonString: "{\"myFloat\":23.2322998046875}") //23.2323998
parseMyFloat(jsonString: "{\"myFloat\":23.2322998}") //23.2323998