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Protocol-based implementation of "Swift currying in practice" (https://medium.com/@NSomar/swift-currying-in-practice-85d3f1064b56)
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| // | |
| // This is copied from Omar's original | |
| // | |
| // Stub post | |
| class Post {} | |
| enum ResponseError: ErrorType { | |
| // The server error has expired, please refresh it | |
| case SessionExpired | |
| // Any other error | |
| case OtherKindOfError | |
| } | |
| // Function to refresh the session | |
| // This function connects to the server and perform a refresh token | |
| func refreshSession(completion: () -> () ) { | |
| completion() | |
| } | |
| typealias CompletionClousure = ([Post]?, ResponseError?) -> () | |
| // Fetch the posts | |
| func fetchPosts(userId: String, completion: CompletionClousure) { | |
| // This is a hack to try out the session expiry | |
| // If post = "123" then session is expired | |
| if userId == "123" { | |
| completion(nil, .SessionExpired) | |
| return | |
| } | |
| let posts = [Post(), Post()] | |
| completion(posts, nil) | |
| } | |
| // | |
| // End copying | |
| // | |
| // | |
| //: ## Protocol implementation | |
| // Simple protocol for all Fetchers | |
| protocol Fetcher { | |
| typealias ResponseType | |
| func fetch(completion: (ResponseType?, ResponseError?) -> ()) | |
| } | |
| // A specific fetcher. We'll reuse fetchPosts, but of course that normally would be encoded here instead. | |
| struct PostFetcher: Fetcher { | |
| let userId: String | |
| func fetch(completion: ([Post]?, ResponseError?) -> ()) { | |
| fetchPosts(userId, completion: completion) | |
| } | |
| } | |
| // This takes a fetcher and returns a fetcher. This composes identically to curried functions. | |
| struct RefreshFetcher<F: Fetcher>: Fetcher { | |
| let base: F | |
| func fetch(completion: (F.ResponseType?, ResponseError?) -> ()) { | |
| // All of this is copied exactly from Omar's work. I just changed "request" to "base.fetch" | |
| base.fetch { (response, error) in | |
| if let error = error where error == .SessionExpired { | |
| refreshSession { | |
| print("Refresshing Session") | |
| self.base.fetch { (response, error) in | |
| // Display the posts | |
| completion(response, error) | |
| } | |
| } | |
| return | |
| } | |
| // Display the posts | |
| completion(response, error) | |
| } | |
| } | |
| init(_ base: F) { self.base = base } | |
| } | |
| // And now we can use it: | |
| PostFetcher(userId: "123").fetch{ posts, error in | |
| print("Use posts to fill UI") | |
| } | |
| // And we can compose with it easily, just like currying. | |
| RefreshFetcher(PostFetcher(userId: "123")).fetch{ posts, error in | |
| print("Use posts to fill UI") | |
| } |
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