A sample function that uses DispatchGroup API

DispatchGroupImplementation.swift

    func dispatchGroups(
        from categoryIdentifiers: [ItunesCategoryIdentifier]) {

        // 1
        let dispatchGroup = DispatchGroup()
        // 2
        var sections: [ItunesCategorySection] = []
        // 3
        for categoryIdentifier in categoryIdentifiers {
            // 4
            dispatchGroup.enter()
            // 5
            service.fetch(Feed<ItunesResources<FeedItem>>.self, itunes: Itunes(mediaTypePath: categoryIdentifier.mediaType)).sink { _ in
                dispatchGroup.leave() // 6
            } receiveValue: { feed in
                             // 7
                let feedItemViewModels = feed.feed?.results.compactMap { FeedItemViewModel(model: $0) } ?? []
                sections.append(ItunesCategorySection(sectionID: categoryIdentifier, cellIDs: feedItemViewModels))
            }.store(in: &cancellables)
        }
        // 8
        dispatchGroup.notify(queue: .main) {
            self.itunesSections = sections.sorted { $0.sectionID.rawValue < $1.sectionID.rawValue }
        }
    }