[Second review] SE-0395: Observability

Evolution Proposal Reviews
48

The macro synthesis for the method withMutation is user-replaceable.

    internal nonisolated func withMutation<Member>(of keyPath: KeyPath<UserInput, Member>, _ mutation: () throws -> T) rethrows {
        defer { if keyPath != \.validValue { onValueChange() } }
        return try _$observationRegistrar.withMutation(of: self, keyPath: keyPath, mutation)
    }

That would replicate what the macro does for mutations and add that value validation. It is worth noting that check on the key path is required to prevent recursion.

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