Map array of objects into another array with Combine not working? - ios

Question

I am subscribing to a #Published array in my view model so I can .map every object appended as an array of PostAnnotations...
I am not able to map the post array into an array of PostAnnotations and get the error:
ERROR MESSAGE: Declared closure result '()' is incompatible
What am I doing wrong??
class UserViewModel: ObservableObject {
var subscriptions = Set<AnyCancellable>()
let newPostAnnotationPublisher = PassthroughSubject<[PostAnnotation], Never>()
#Published var currentUsersPosts: [Posts] = []
func addCurrentUsersPostsSubscriber() {
$currentUsersPosts
// convert each post into a PostAnnotation
.map { posts -> [PostAnnotation] in
// ^ERROR MESSAGE: Declared closure result '()' is incompatible
//with contextual type '[SpotAnnotation]'
posts.forEach { post in
let postAnnotation = PostAnnotation(post: post)
return postAnnotation
}
}
.sink { [weak self] postAnnotations in
guard let self = self else { return }
// send the array of posts to all subscribers to process
self.newPostAnnotationsPublisher.send(postAnnotations)
}
.store(in: &subscriptions)
}
func loadCurrentUsersPosts() {
PostApi.loadCurrentUsersPosts { response in
switch response {
case .success(let posts):
self.currentUsersPosts.append(contentsOf: spots)
case .failure(let error):
//////
}
}
}
}

Answer 1

forEach doesn't return a value. You want map, which returns a new collection based on the transform performed inside the closure:
.map { posts -> [PostAnnotation] in
posts.map { post in
let postAnnotation = PostAnnotation(post: post)
return postAnnotation
}
}
Or, even shorter:
.map { posts -> [PostAnnotation] in
posts.map(PostAnnotation.init)
}
And, even shorter (although, I'd argue that it starts losing readability at this point):
.map { $0.map(PostAnnotation.init) }