A lot of times when working in a team, you would write a class, or add an enumeration to an existing class or add a new property. Some times, you might need to tell other programmers who work on the same code-base that a property, enumeration or a method that you wrote is now becoming deprecated and perhaps a new version of the API introduces a new property/enumeration/method that programmers need to use instead.
This is where LLVM can be very useful. Obviously, if you are the only programmer in a project and not developing an API for others, this might not be of much use to you. But if you are used to working in a team, knowing this trick is an absolute necessity.
Let’s say we are writing an enumeration that at the time of writing (let’s assume at the time of writing this enumeration, iOS 5 was the latest iOS version), everything was fine like so:
Now let’s say iOS 6.0 is introduced and you are thinking to yourself “Oh that Ultra Fast item in the enumeration is just not very good and I think I have to remove it”. So what to do now? The solution is using __attribute__ like so:
The availability attribute can have the following keys:
introduced: this will be the version of the operating system (iOS, Mac OS X) where the API was introduced first.
deprecated: this is the version of the operating system where the API was deprecated (ready to be removed from the API in later versions of the API)
obsoleted: the version of the operating system where the API is completely removed and is no longer supported.
message: the message to display to the programmer in Xcode.
As you can see, right in front of the availability attribute, we can write “ios” or “macosx” to denote if an API is (un)available for iOS or Mac OS X respectively.
Now let’s assume iOS 7.0 comes along and we want to completely stop our support for the “ultra fast” enumeration value. All we have to do is to add the “obsoleted” key to the availability attribute like so: