Hero list presenter class

HeroListPresenter.swift

final class HeroListPresenter: Presenter {
    
    private let service: HeroService
    weak private var view : HeroListView?
    ...
    init(service: HeroService) {
        self.service = service
    }
    
    func attachView(view: HeroListView) {
        self.view = view
    }
    ...
    func getHeroes() {
        self.view?.startLoading()
        service.getHeroes { [weak self] heroes in
            self?.view?.finishLoading()
            if heroes.count > 0 {
                let mappedHeroes = heroes.map {
                    return HeroViewData(hero: $0)
                }
                self?.heroes.append(contentsOf: mappedHeroes)
                self?.view?.reloadHeroList()
            } else {
                self?.view?.showEmptyListMessage()
            }
        }
    }
}