BAD_INSTRUCTION within swift closure - closures

Question

func loadMe() -> Void {
println(me.initUrl());
let url:NSURL = NSURL(string:me.initUrl())
let request:NSURLRequest = NSURLRequest(URL:url)
let queue:NSOperationQueue = NSOperationQueue()
NSURLConnection.sendAsynchronousRequest(request, queue:queue, completionHandler:{response, data, error in
if data {
var jerr:NSError?
var json:NSDictionary = NSJSONSerialization.JSONObjectWithData(data, options:NSJSONReadingOptions.MutableContainers, error:&jerr) as NSDictionary
if !jerr {
println(json.description)
let time:String = json.valueForKey("time") as String
println(time)
// self.me.setDictionary(json)
}
}
})
}
The code above works fine up to the point where i want to assign a value from an NSDictionary to a variable.
let time:String = json.valueForKey("time") as String
is followed by EXC_BAD_INSTRUCTION(code=EXC_I386_INVOP,subcode=0x0) but
println(json.description)
prints out a valid NSDictionary. Does anybody know a solution to this problem?

Answer 1

The valueForKey() method returns an optional value; you are forcing that value to a String and apparently that is causing the crash. I can get the Swift REPL to crash with:
1> var json = ["a": "1", "b": "2"]
json: Dictionary<String, String> = {
[0] = {
key = "a"
value = "1"
}
[1] = {
key = "b"
value = "2"
}
}
2> let data:String = json["b"] as String
Bitcast requires both operands to be pointer or neither
%58 = bitcast i8* %57 to %SS.232
Bitcast requires both operands to be pointer or neither
%110 = bitcast i8* %109 to %SS.232
Stored value type does not match pointer operand type!
store %SS.232 %110, i8** %.core7._baseAddress.value, align 8
i8*LLVM ERROR: Broken function found, compilation aborted!
Assertion failed: (err == 0), function ~Mutex, file /SourceCache/lldb_KLONDIKE/lldb_KLONDIKE-320.3.100/source/Host/common/Mutex.cpp, line 246.
Abort trap: 6
The solution is to forgo the String coercion. In my example:
2> let data:String? = json["b"]
data: String? = "2"
3> let data:String? = json["c"]
data: String? = nil
I suspect you added the 'as String' 1) knowing that the value is actually a String and 2) to avoid a compiler error. The proper approach is to use ? to indicate an optional value.

Answer 2

I solved my problem with casting to the correct type of the original NSDictionary value after i realised that not all values of the NSDictionary were NSStrings. If your service returns a mixed type JSON object like this
{"id":2, "name":"AC Vent Temp", ...}
you'll have to fetch it's values like that.
var id:int = sensor.valueForKey("id") as Int;
var name:String? = sensor.valueForKey("name") as String;