A sample `AddressService`.

address_service.swift

final class AddressService { /// (1) A hypothetical address service that exposes a publisher of `Address`s,
/// both from GPS and manual entry.

	// MARK: - Inputs

	let addressEntry = PassthroughSubject<Address, AddressError>() /// (2) For sake on example, let’s imagine a
	/// `TextField` is bound to this subject so that in a location-related application, users can _manually_
	/// enter an address.

	// MARK: - Outputs

	let addressToDisplay: AnyPublisher<Address, AddressError> /// (3) A publisher that merges[^1] both manual
	/// address entry and those from the network.

	/* … */

	init() {
		addressToDisplay = guessedAddressFromGeolocaton()
			.multicast(subject: addressEntry) /// (3) Leaning on the `multicast(subject:)` overload.
			.autoconnect()^ /// (4) Two notes here. First, `multicast` returns a `Publishers.Multicast`,
			/// which conforms to the [`ConnectablePublisher` protocol](https://developer.apple.com/documentation/combine/connectablepublisher).
			/// I’ll dig into what this means, below, but for now, this `autoconnect` call restores
			/// ordinary `Publisher` behavior.
			///
			/// And second, the operator in the room, `^`. It’s postfix shorthand for `eraseToAnyPublisher`.
			/// I know custom operators can be a holy war, but I discussed my liking of this one in an
			/// [earlier diary entry](https://jasdev.me/notes/postfix-erasure).

		/* … */
	}
}

private func guessedAddressFromGeolocaton() -> AnyPublisher<Address, AddressError> { /* … */ } /// (5) A publisher that
/// emits address guesses based on location.

/// [^1] (footnote from `(3)`): Another approach to `init`’s body is to lean on the
/// [`merge` operator](https://developer.apple.com/documentation/combine/publisher/3204724-merge).
/// And, we could! But, to do so, safely, we’d need to rely on `share`, which is what I’m trying to
/// sketch out.
///
/// For the curious,
///
/// ```swift
/// addressToDisplay = guessedAddressFromGeolocaton()
/// 	.share()
/// 	.merge(with: addressEntry)^
/// ```