Gist showing the difference between the property wrapper `@Published` and a `CurrentValueSubject`

CombinePublishedVsCurrentValueSubject.swift

//
//  CombinePublishedVsCurrentValueSubject.playground
//
//  Created by Felix Mau on 09.02.21.
//  Copyright © 2021 Felix Mau. All rights reserved.
//

import Foundation
import Combine

class PublishedTest {

    /// > When the property changes, publishing occurs in the property’s `willSet` block,
    /// > meaning subscribers receive the new value before it’s actually set on the property.
    /// https://developer.apple.com/documentation/combine/published
    @Published
    var numberOfAdults: Int = 0
}

class SubjectTest {

    var numberOfAdults: Int {
        get { numberOfAdultsSubject.value }
        set { numberOfAdultsSubject.value = newValue }
    }

    var numberOfAdultsPublisher: AnyPublisher<Int, Never> {
        numberOfAdultsSubject.eraseToAnyPublisher()
    }

    private let numberOfAdultsSubject = CurrentValueSubject<Int, Never>(0)
}

var subscriptions = Set<AnyCancellable>()


// MARK: - `@Published` Test

let publishedTest = PublishedTest()
publishedTest.$numberOfAdults.sink { [weak publishedTest] in
    print("@Published: Value passed to closure", $0)
    print("@Published: Value on class property", publishedTest!.numberOfAdults) // <- As `@Published` uses `willSet` the value is not updated here.
}.store(in: &subscriptions)

publishedTest.numberOfAdults = 1
publishedTest.numberOfAdults = 2

// Output
//
// @Published: Value passed to closure 0
// @Published: Value on class property 0
// @Published: Value passed to closure 1 ‼️
// @Published: Value on class property 0 ‼️
// @Published: Value passed to closure 2 ‼️
// @Published: Value on class property 1 ‼️
//
// -> Closure gets informed with initial value, therefore it seems like `@Published` uses a `CurrentValueSubject` internally.


// MARK: - `CurrentValueSubject` Test

let subjectTest = SubjectTest()
subjectTest.numberOfAdultsPublisher.sink { [weak subjectTest] in
    print("CurrentValueSubject: Value passed to closure", $0)
    print("CurrentValueSubject: Value on class property", subjectTest!.numberOfAdults)
}.store(in: &subscriptions)

subjectTest.numberOfAdults = 1
subjectTest.numberOfAdults = 2

// Output
//
// CurrentValueSubject: Value passed to closure 0
// CurrentValueSubject: Value on class property 0
// CurrentValueSubject: Value passed to closure 1
// CurrentValueSubject: Value on class property 1
// CurrentValueSubject: Value passed to closure 2
// CurrentValueSubject: Value on class property 2