Add ability to subscribe to multiple keys and to prevent propagation

[fredyshox]

Attempt to fix #30

Added CompositeUserDefaultsKeyObservation for observing multiple keys, with preventPropagation option to prevent infinite recursion when change is made within handler.

I store flag in threadDictionary of the current thread to determine when changes should be propagated. This enables to still support changes made on other threads, while initial one is still processing handler (more in testObservePreventPropagationMultiThread test case).

Code is still a little messy, but let me know what you think :)

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IssueHunt Summary

Referenced issues

This pull request has been submitted to:

• #30: Add ability to subscribe to multiple keys or any change in a given suite

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[fredyshox]

As for observeAll and publisherAll for all known keys, Mirror does not yet support static fields, so my initial thought of Mirror(Defaults.Keys.self).children doesn't work.

[sindresorhus]

This is looking promising. Thanks for working on it. 🙌

[sindresorhus]

As for observeAll and publisherAll for all known keys, Mirror does not yet support static fields, so my initial thought of Mirror(Defaults.Keys.self).children doesn't work.

Too bad. "static" always lags behind in functionality. We could actually solve this without mirror if we switch to using Key paths instead of the dot syntax (It would then be Defaults[\.foo]. But of course "static key paths" are not yet implemented in Swift.

[sindresorhus]

Is there any way we could add propagation prevention to publisher(keys:) too?

[fredyshox]

Is there any way we could add propagation prevention to publisher(keys:) too?

We could do that, by tweaking DefaultsSubscription into using new CompositeUserDefaultsKeyObservation. But there're few catches. Note that preventPropagation won't protect you, if you use dispatch.async inside observation handler. And in Combine is far more common to use things like receive(on:), debounce, delay etc.

[fredyshox]

I’ve came up with a different approach, to make this feasible on both classic and combine implementations. A block based approach inspired by SwiftUIs withAnimation:

func withNoPropagation(block: () -> Void) {
	// tweak threadDictionary and call block
}

Every change made in the block, would not be propagated at all. Usage example:

Defaults.observeAll(.key1, .key2) {
	// …
	withNoPropagation {
		// update some value at .key1
		// this will not be propagated
		Defaults[.key1] = 11
	}
	// this will be propagated
	Defaults[.someKey] = true 
}

A big advantage is that, this may be used not only in observation callback, but also in Combine callbacks (regardless of publisher modifiers) or any other place.

I’ve working implementation, let me know what you think 👍

[sindresorhus]

@fredyshox That's a good approach! I like it.

Should it be withNoPropagation or withoutPropagation?

[sindresorhus]

Also replied to #49 (comment).

[sindresorhus]

Sorry for the late reply. Summer and COVID made it hard to keep up with all the PRs.

[sindresorhus]

Can you document withoutPropagation?

[fredyshox]

I've added docstrings to new public API and updated readme. Also added short comment explaining inner workings of preventPropagation inside its implementation 🙂.

[sindresorhus]

This is looking great. Nice work as always 🙌🏻

[sindresorhus]

@fredyshox Would you be interested in joining the project as a maintainer? There's no commitment needed. Just want to highlight your contributions with your name in the readme. No worries if not though.

[fredyshox]

Yes I do! Feel free to mention me :)