Latest 0.3.0
License MIT
Platforms ios 8.0, osx 10.11, watchos 2.0, tvos 9.0
Dependencies Alamofire, SwiftyJSON, PromiseKit/Alamofire

Protocol-oriented networking in Swift with promises



Neutron is a wrapper around Alamofire that promotes protocol-oriented Swift networking.

Networking in Swift usually involves a tediously long list of static functions in a networking "manager" class, with each function doing repetitive calls to other functions. Worse, information about each request is often scattered across different places (routes may be in one enum, parameter keys may be in another, etc.). With Neutron, you define requests in structs called Quarks:

Defining a Quark:

struct Login: Quark {
    typealias ResponseType = User

    let username: String, password: String

    let route = "/login"
    var parameters: Parameters = [
        return [
            "user": username,
            "pass": password

    func process(response: Data) throws -> User {
        let user = ...
        return user

Forming and making the request:

Login(username: "user", password: "****").make()
    .then { user in
        print("Got user:", user)
    .catch { error in

That’s it. Since Quark is a protocol, structs and promises (see PromiseKit), make it easy to define, form, and make the network request. Aside from default request data, everything about the request is contained in the struct.

Ultimately, Neutron improves upon the traditional network manager paradigm with:

  • [x] Expressive, self-contained requests
  • [x] Unverbose code due to default protocol implementations
  • [x] Composability thanks to protocol inheritance
  • [x] Auto-generated memberwise initializers for requests
  • [x] Modular, organizable network requests


Defining Quarks

A Quark is a struct that conforms to the Quark protocol or a protocol which inherits from it:

import Neutron

struct MyQuark: Quark {
    <response type>
    <process method>

There are three parts to this, the order of which does not really matter:

1. Define response type

In the struct, you should provide a typealias to ResponseType that specifies what kind of response you ultimately expect to be returned:

typealias ResponseType = MyModelClass

This will be the type that the process method (described below) must return and that the promise will return.

2. List properties

List out the properties your request will require, careful not to override the protocol properties below. Swift automatically generates an initializer for these uninitialized properties. For instance, a request to renaming a to-do in a to-do list may required the id and title of the to-do:

let id: Int
let title: String


let id: Int, title: String

Use these properties to produce any of the following protocol properties to form the request:

host: String (default is "http://localhost")

route: String (no default – required)

apiVersion: APIVersion (default is .none)

parameters: Parameters (default is [:])

encoding: ParameterEncoding (default is URLEncoding.default)

headers: HTTPHeaders (default is [:])

If a property has a default, then it should be omitted when defining the request. In order to use your own properties in the request, you need to use computed variables:

var route: String {
    return "/todo/(id)" // id defined earlier

var parameters: Parameters = [
    return [
        "title": title // title defined earlier

It is suffice to define other static properties as let properties. Note that if you do not initialize required protocol properties, they show up in the generated initializer.

3. Process response

Lastly, implement the required func process(response: Data) throws -> ResponseType function. This method is called if the network request succeeds in order to convert the response body into the proper ResponseType as defined earlier. It is a throwing method since the response data may not be as our client application expects.

With the to-do renaming example, if the server returns a JSON of the new todo, we might write the process method as such, using SwiftyJSON:

func process(response: Data) throws -> Todo {
    let json = JSON(data) // unnecessary, see 'Custom Quarks'
    guard let id: Int = json["id"].int,
        let title: String = json["title"].string else {
        throw NeutronError.badResponseData // throw error if unexpected data

    return Todo(id: id, title: title, ... )

Forming Quarks

Forming a request is as easy as calling the Swift-generated "memberwise" initializer:

RenameTodo(id: id, title: title)

Since requests are structs, they’re storable, copyable, and modifiable:

let renameRequest = RenameTodo(id: id, title: title)
let copy = renameRequest

Making the Quark Requests

Finally, you just want to make requests. Call the make function on the request, which returns a PromiseKit promise, and handle it accordingly:

RenameTodo(id: id, title: title).make()
    .then { todo in
        // use updated todo
    .catch { error in
        // catch any error that occurred

Custom Quarks

It may be concerning that the default host for requests is localhost, and that the process method has a parameter of type Data and not something like JSON. This is where protocol composability comes in!

You can use the JSONQuark protocol for requests that are sure to return SwiftyJSON JSON. With JSONQuark, the response parameter in the process method is of type JSON instead of Data.

You can provide your own protocol requirements and default implementations when you create your protocol that inherits from Quark or a sub-protocol of it, like JSONQuark:

protocol TodoQuark: Quark {
    var authToken: String { get } // every request should provide one

extension TodoQuark { // custom default implementations
    var host: String {
        return "https://my.todo.list.server"

    var headers: HTTPHeaders = [
        "auth": authToken

Beautiful, no?


If we so choose, requests can be nested inside our models as RESTful resource requests:

class BlogPost { ... }
extension BlogPost {
    struct Get: Quark { ... }
    struct Post: Quark { ... }
    struct Delete: Quark { ... }

// Later...

Example Project

To run the example project, clone the repo, and run pod install from the Example directory first.


Requires Swift 3.0 or above


Neutron is available through CocoaPods. To install
it, simply add the following line to your Podfile:

pod "Neutron"

Todo List

  • [ ] README documentation
  • [ ] Testing and CI
  • [ ] Swift 2.x compatability
  • [ ] More Quarks
  • [ ] Configuration and documentation in Neutron.swift
  • [ ] Remove dependencies and make them optional subspecs


This is a very young project, so forgive the mess and/or lack of functionality. That said, contributors would be great to have!

Daniel Li, [email protected]


Neutron is available under the MIT license. See the LICENSE file for more info.

Latest podspec

    "name": "Neutron",
    "version": "0.3.0",
    "summary": "Promise-based, protocol-oriented network requests in Swift",
    "homepage": "",
    "license": {
        "type": "MIT",
        "file": "LICENSE"
    "authors": {
        "Daniel Li": "[email protected]"
    "source": {
        "git": "",
        "tag": "0.3.0"
    "platforms": {
        "ios": "8.0",
        "osx": "10.11",
        "watchos": "2.0",
        "tvos": "9.0"
    "source_files": "Sources/**/*",
    "dependencies": {
        "Alamofire": [],
        "SwiftyJSON": [],
        "PromiseKit/Alamofire": []
    "pushed_with_swift_version": "3.0"

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