PhotoListViewModel.swift

enum PhotoListConstant {
    static let listURL = "https://jsonplaceholder.typicode.com/photos"
}

enum NetworkError: Error {
    case invalidURL
}

final class PhotoListViewModel: ObservableObject {
    @Published var photoItems = [PhotoItemModel]()
    
    @MainActor // 4
    func fetchPhotoList() async {
        guard let url = URL(string: PhotoListConstant.listURL) else {
            fatalError(NetworkError.invalidURL.localizedDescription)
        }
        do {
            // 5
            let (data, _) = try await URLSession.shared.data(from: url)
            let photoListData = try JSONDecoder().decode([PhotoItemModel].self, from: data)
            // 6
            self.photoItems = photoListData
        } catch let error {
            fatalError(error.localizedDescription)
        }
    }
}