Deprecate `.observe()` about defaults HOT 3 OPEN

I wanted the main method to be simple, because from extensive use, I almost never needed the old value. However, I do agree we should support providing the old value somehow. Maybe a updatesWithPrevious() method or something. It would return a tuple of old/new values though. I considered overloading .updates(), but it may create some ambiguities. I will need to think about it.

For now, you could use these utilities:

extension AsyncStream {
	func withPrevious() -> AsyncStream<(previous: Element?, current: Element)> {
		.init { continuation in
			Task {
				var previous: Element?
				for await element in self {
					continuation.yield((previous, element))
					previous = element
				}

				continuation.finish()
			}
		}
	}

	func withPrevious(initialPreviousValue: Element) -> AsyncStream<(previous: Element, current: Element)> {
		.init { continuation in
			Task {
				var previous = initialPreviousValue
				for await element in self {
					continuation.yield((previous, element))
					previous = element
				}

				continuation.finish()
			}
		}
	}
}

The obvious benefit of having support built-in is that the previous value would be non-optional.

from defaults.

Since I see the point to get rid of dead wood and streamline the API, I see a strong benefit of using .observe() and that is the KeyChange object, which comprises KeyChange.oldValue. AsyncStream would loose this functionality.

from defaults.

Would it make sense to extend the AsyncStream implementation with a KeyChange next to Value?

from defaults.