Error Hierarchy

This is a sibling framework to ActionHierarchy, but specialized for Error handling.

Using a closure contained in EnvironmentValues, View objects that are lower in the hierarchy report Error objects up the view hierarchy, while views that are higher in the hierarchy use one of the modifiers to register themselves as a responder to receive, transform, or handle the Error objects.

Triggering an Error

Errors are triggered using the reportError closure added to EnvironmentValues.

Example:

struct MyError: Error {}

struct TriggerView: View {
	@Environment(\.reportError) var reportError
	
	var body: some View {
		Button("Trigger") {
			reportError(MyError())
		}
	}
}

Receiving, Handling and Transforming an Error

There are three kinds of operations that can be applied to an Error that has been triggered. All of these are executed by registering a closure the same way you would apply a view modifier to a View.

struct ContentView: View {
	var body: some View {
		TriggerView()
			.receiveError { .notHandled }
			.transformError { MyError() }
			.handleError {}
	}
}

All of these functions have a generic version that receives the type of an Error as the first parameter, only errors matching the provided type will be acted on, any other error will be propagated up the view hierarchy.

struct ContentView: View {
	var body: some View {
		TriggerView()
			.handleError(MyError.self) {}
	}
}

Receiving an Error

When receiving an Error, it’s up to the registered closure to determine whether the Error has been fully handled or not.

If the registered closure returns .handled, the Error will no longer be propagated up the view hierarchy.
If it returns .unhandled instead, the Error will continue to be propagated.

Handling an Error

Any error that is handled will no longer be propagated up the view hierarchy. This is equivalent to using a receiveError closure that always returns .handled.

Transforming an Error

Transforming functions can be used to replace the received Error. It could be an Error of a different type, or an Error of the same type but with different values.

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