While learning Cocoa Touch frameworks from the new Apple documentation I've noticed that over time some functions get deprecated which appears with a strike-through line in the documentation. As engineers or developers, how do you guys find out why a function was deprecated and most importantly how do you find the new options that are available if there are any?
An example is AVAudioPlayerDelegate where two functions have been deprecated for handling audio interruptions: AVAudioPlayerDelegate Apple Documentation
I searched for ios developer release notes and found this link
The why always comes from improvement. The improvement could be in terms of performance, readability, new features, bugs & errors, new members with a different approach who come to write the language.
As a developer you should follow the release notes of every new iOS version, over the course of following 2-3 versions you get a better grip on the whole thing also keep in mind that the compiler is smart and sometimes by typing old code it would pop new syntax as a suggestion or you can use migration tools.