Question

I’m an objective-c programmer and I’m wondering how low should I go (methods wise).

For example, there’s NSURL then CFURL (which is lower). I’m not sure whether using lower or higher levels will add more functionality, or are faster.

Answer 1

The Foundation (NSURL) framework classes are often based on the code in CoreFoundation (CFURL).

With CF types you generally work with opaque structs, operating on the data by using related functions. If you needed to write pure c code then you would need to use CF. Otherwise these can be a bit clunky and difficult to use in places.

Objective-C classes also allow you to do additional thing like add categories etc.

Toll-Free bridging

There are times when you may need to mix and match your code slightly and it’s handy to know that a lot of types can simply be cast. e.g. an NSString could be used instead of an CFStringRef

An example of when I had to do this recently was when I needed to do some url encoding (the NSString stringByAddingPercentEscapesUsingEncoding: didn’t quite cut it) . The function required CFStringRef‘s, but with a simple cast I could use my NSString‘s

CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault, 
                                        (CFStringRef)stringToEncode, // <- NSString
                                        NULL,
                                        (CFStringRef)encodeChars,    // <- NSString
                                        kCFStringEncodingUTF8)

Generally you can get away with and you should where possible use the Foundation classes (higher level of abstraction) as they will most likely provide the same functionality. There will of course be different scenarios where this is not the case, like the url encoding I had to do.