Better completion blocks by using higher order functions

Completion.swift

func completion<Result>(onResult: @escaping (Result) -> Void, onError: @escaping (Error) -> Void) -> ((Result?, Error?) -> Void) {
    return { (maybeResult, maybeError) in
        if let result = maybeResult {
            onResult(result)
        } else if let error = maybeError {
            onError(error)
        } else {
            onError(SplitError.NoResultFound)
        }
    }
}

// Use where a completion block will give a `Bool` value indicating it was successful or not.
func completion(onSuccess: @escaping () -> Void, onFailure: @escaping () -> Void) -> ((Bool) -> Void) {
    return { success in
        if (success) {
            onSuccess()
        } else {
            onFailure()
        }
    }
}

enum SplitError: Error {
    case NoResultFound
}

@Monserg

I'm assuming that if you get no ResponseAPIType back then that is an error? In that case, you could refactor like this:

public func executeGET(byMethodAPIType methodAPIType: MethodAPIType, onComplete: @escaping (ResponseAPIType) -> Void, onError: @escaping () -> Void) {
  let response = // do the work here
  if let response = response {
    onComplete(response)
  } else {
    onError()
  }
}

However, if you can get a ResponseAPIType which contains an error then you will have to refactor a little differently.

Hope that helps!