ImageResolver.swift

final class ImageResolver: ObservableObject {
    @Published var image: CGImage? = nil

    ...    
    
    func fetchImage() -> CGImage? {
        return fetchPreviewImage(imageName: name, size: size, fetcher: fetch)
    }

    private func fetch() -> CGImage? {
        if image != nil {
            return image
        }
        imageFetchable.fetchImage(name: name, size: size)
            .sink( ... )
            .store(...)
        return image
    }

    ...
}