fake va_list in ARC
EDIT: This no longer works. As foreseen in the initial answer, the ABI appears to have changed out from under this answer
Played around for a bit and got it to work -- Double checked for leaks or abandoned memory and didn't see any.
NSArray *fixedArguments = [[NSArray alloc] initWithObjects: @"foo", @"bar", @"baz", nil]; NSRange range = NSMakeRange(0, [fixedArguments count]); NSMutableData* data = [NSMutableData dataWithLength: sizeof(id) * [fixedArguments count]]; [fixedArguments getObjects: (__unsafe_unretained id *)data.mutableBytes range:range]; NSString* content = [[NSString alloc] initWithFormat: @"1: %@ 2: %@ 3: %@" arguments: data.mutableBytes]; NSLog(@"%@", content);
I like to (ab)use NSMutableData like this to get retain/release semantics on an arbitrary chunk of memory -- It's not necessarily relevant to the issue at hand, but it's a neat little trick.
As a note to future readers: Faking up a va_list like this happens to work with the current ABI for MacOS and iOS, but in general it's not portable, and not a good approach.
Its possible if you are willing to add a little bit of swift to your project!
The important bit is the mapping of NSArray to [CVarArgType]
which is the swift equivalent for va_list
. If you try to cast [AnyObject]
to [CVarArgType]
you cause run time crashes, but with the map
we can explicitly make the needed list.
The rest of the code is the wrapper I made so that I can call this from obj-c. You could make a wrapper for any obj-c function that you want to call in this way.
@objc class StringFormat: NSObject { class func format(key: String, args: [AnyObject]) -> String { let locArgs: [CVarArgType] = args.map({ (arg: AnyObject) -> CVarArgType in if let iArg = (arg is NSNumber ? arg.intValue : nil) { return iArg } return arg as! CVarArgType }); return String(format: key, arguments: locArgs) }}