A Swift property wrapper which conforms to Publisher and emits before the wrappedValue has been set

NextValue.swift

import Combine

@propertyWrapper
struct NextValue<Output> {
	typealias Failure = Never
	typealias Publisher = AnyPublisher<Output, Never>
	
	var wrappedValue: Output {
		willSet {
			subject.send(newValue)
		}
	}
	
	var projectedValue: Publisher {
		subject.eraseToAnyPublisher()
	}
	
	private let subject = PassthroughSubject<Output, Never>()
	
	init(initialValue: Output) {
		self.wrappedValue = initialValue
	}
}

Usage:

import Combine
import SwiftUI

final class ContentViewModel: BindableObject {
	@NextValue var model = "Foo Bar"
	var willChange: NextValue<String>.Publisher { $model }
}