Odtnhj

I've developed this generic method to execute requests:

func executeRequest<T, S, E>(_ request : RequestBuilder<T>,
 map: (@escaping (T) -> S)) -> RepositoryResult<S, E> {
 return RepositoryResult().doTask result in
 request.execute (response, error) in
 // do some stuff
 result.notifySuccess(value: map(body))
 

My map function is defined in a subclass with generic types:

class BaseMapper<R, U> 
 class func transform(_ dataModel:R) -> U 
 fatalError("Override this method")
 
 // other generic methods


class HomeMapper:BaseMapper<HomeDTO, Home> 
 override class func transform(_ dataModel: HomeDTO) -> Home 
 return Home(customerFirstName: dataModel.customerFirstName,
 balance: MoneyMapper.transform(dataModel.balance),
 accounts: AccountSummaryMapper.listTransform(dataModel.summaries))
 

If I call the request executor method passing directly the map function like that:

 func getHomeInfo() -> RepositoryResult<Home, HomeError> 
 return executeRequest(HomeAPI.getMyHomeWithRequestBuilder(), map: HomeMapper.transform)
 

I believe Swift compiler is crashing because it returns several random errors: "Segmentation fault: 11". Otherwise, if I call the method specifying the "S" return type, it works:

func getHomeInfo() -> RepositoryResult<Home, HomeError>
 return executeRequest(HomeAPI.getMyHomeWithRequestBuilder(), map: (homeDTO) -> Home in
 HomeMapper.transform(homeDTO)
 )
 

Furthermore, using a Mapper that doesn't inherit from BaseMapper and passing the function directly, it also works. Another thing that I don't understand is that RxSwift has a map function that works calling it with my first option...

Why swift compiler cannot infer "S" type? Why swift compiler is crashing and can't tell which line is crashing and why?

I've found a solution: associatedtypes

protocol Mappable 
 associatedtype T
 associatedtype S

 static func transform(_ dataModel:T) -> S


class MapperHome : Mappable 
 static func transform(_ dataModel: HomeDTO) -> Home 
 return Home(customerFirstName: dataModel.customerFirstName,
 balance: MoneyMapper.transform(dataModel.balance),
 accounts: AccountSummaryMapper.listTransform(dataModel.summaries))
 


func getHomeInfo() -> RepositoryResult<Home, HomeError>
 return executeRequest(HomeAPI.getMyHomeWithRequestBuilder(), map: MapperHome.transform)

I don't understand why this code compiles and using inheritance instance of implementation of a protocol it doesn't... I don't know if it's a compiler bug or my fault.