Functional chaining and promises in Swift
Swift Objective-C Ruby
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Forbind Mac
Forbind tvOS
ForbindExtensions Mac
ForbindExtensions tvOS


Functional chaining and promises in Swift

Note: still in an experimental state. Everything could change. I would love some feedback on this. Write to @ulrikdamm on Twitter.

What is it

Bind local or async expressions together functionally, all error handling taken care of for you:

func getUser(id : String) -> Promise<Result<User>> {
	let data = NSURL(string: id)
		=> { NSURLRequest(URL: $0) }
		=> NSURLConnection.sendRequest(.mainQueue())
		=> { response, data in data }
	return data
		=> NSJSONSerialization.toJSON(options: nil)
		=> { $0.dictionaryValue }
		=> User.fromJSON

• Bind operations together with =>

• No error handling inside your logic

• Transparent async calls

• No if-lets

• Combine inputs with ++

For more details, read my Blog post.

New in 1.1

• ResultPromise and OptionalPromise has been replaced with Promise<Result> and Promise<T?>. Still works the same.

• You can use the bind operator to map over lists of promises!

let user = User(name: "Ulrik")
let names = user.loadFriends() => { $ } // [Promise<String>]

• And you can also filter and reduce with filterp and reducep:

let someNames = filterp(names) { $0 != "Peter" } // Promise<[String]>

• The NSJSONSerialization extension now returns a JSONResult, which is either a Dictionary or Array.

Get started

You can add Forbind to your project using CocoaPods. Just add it to your Podfile:


pod 'Forbind', '~> 1.1'
pod 'ForbindExtensions', :git => ''

(You need the use_frameworks! since that feature of CocoaPods is still in beta. ForbindExtensions are optional)

Or you can add it using Carthage by adding this to your cartfile:

github "ulrikdamm/Forbind" ~> 1.0

This will add both Forbind.framework and ForbindExtensions.framework, which you can drag into your Xcode project.

Then in your files just import Forbind and optionally ForbindExtensions

import Forbind
import ForbindExtensions

The Forbind library is the bind operator (=>) and the combine operator (++), along with the Result enum and Promise classes.

ForbindExtensions are extensions to Foundation and UIKit for working better with Forbind, by, for example, returning a promise instead of using a completion block. The ForbindExtensions are still a work in progress, so you might want to make your own extensions instead. In this case, just only include the Forbind framework.

What is the state of the project?

It’s still very experimental, so I would love some feedback on it. I wouldn’t recommend relying on this for product code yet. If you have a good idea, or just questions, submit a pull request or contact me at @ulrikdamm on Twitter.

Things that still needs to be considered:

• General direction of the project (are there some fundamental flaws?)

• Promise cancellation (support for cancelling an async operation if a promise is deallocated)

• Handling of dispatch queues (currently promise callbacks are run on the same queue as the operation finished on)

• More extensions for common UIKit/AppKit/Foundation methods to use Promise and Result instead of NSErrorPointer and completion blocks.

• "Expression was too complex to be solved in reasonable time" for big expressions.