I am looking at some sample code from some Apple Developer sample projects and I see this pattern repeating quite a few times.

So there is a view controller...

class CameraViewController: UIViewController {
}

and then there is always some extension to that as something like:

extension CameraViewController: AVCaptureVideoDataOutputSampleBufferDelegate {
   ...
}

I am wondering why it is done like this? Is this to allow reusability of the initial defined classes or is there some other reason?

CodePudding user response：

If it's in the same file, it's just for code organization purposes. It's convenient to keep methods together that relate to a specific protocol. It's a good reminder not to change the names of those methods, and it makes clear why a method might seem never to be called (since it's called from Apple code, for example).

If it's in another file, it's sometimes to simplify code-reuse, particularly if a very general-purpose type is conformed to a very app-specific protocol. But even in that case, it may just be for organizational purposes, to make files smaller, or just to express that you consider this to be non-core functionality.

But broadly, extensions are a very common and general-purpose tool that you can use whenever you find them convenient and meaningful.