Combine: Convert Closure into Publisher

Question

How to convert:

func getResults(completion: ([Result]?, Error) -> Void)

Into

var resultsPublisher: AnyPublisher<[Result], Error>

Just a scheme how I see it is (this syntax doesn't exist):

var resultsPublisher: AnyPublisher<[Result], Error> {
  let publisher: AnyPublisher = ... // init
  getResults { results, error in
     guard let results = results else {
       publisher.produce(error: error) // this syntax doesn't exist
       return
     }

     publisher.produce(results: results)  // this syntax doesn't exist

  }

  return publisher
}

I need that because some 3d party SDKs use completion closures and I want to write extensions to them that return Publishers.

Answer 1

The answer is Future Publisher as matt explained:

var resultsPublisher: AnyPublisher<[Result], Error> {
    // need deferred when want 
    // to start request only when somebody subscribes 
    // + without Deferred it's impossible to .retry() later
    Deferred { 
        Future { promise in
           self.getResults { results, error in
              guard let results = results else {
                 promise(.failure(error))
                 return
              }

              promise(.success(results))
           }
         }
    }
    .eraseToAnyPublisher()
}