Ergo

Ergo is a framework for concurrent programming based on promise pipelining. It could help to avoid callback hell in complex asynchronous task

Example

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

Requirements

• Swift 5.0 or higher (or 5.3 when using Swift Package Manager)
• iOS 10 or higher

Only Swift Package Manager

• macOS 10.10 or higher
• tvOS 10 or higher

Installation

Cocoapods

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

pod 'Ergo', '~> 1.4.0'

Swift Package Manager from XCode

• Add it using XCode menu File > Swift Package > Add Package Dependency
• Add https://github.com/hainayanda/Ergo.git as Swift Package URL
• Set rules at version, with Up to Next Major option and put 1.4.0 as its version
• Click next and wait

Swift Package Manager from Package.swift

Add as your target dependency in Package.swift

dependencies: [
  .package(url: "https://github.com/hainayanda/Ergo.git", .upToNextMajor(from: "1.4.0"))
]

Use it in your target as Ergo

 .target(
  name: "MyModule",
  dependencies: ["Ergo"]
)

Author

Nayanda Haberty, hainayanda@outlook.com

License

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

Basic Usage

Ergo utilize the Thenable protocol which is implemented in the Promise class that acts as a proxy for the concurrent task. To create a concurrent task in Promise, just call the runPromise global method with any task you want to run:

runPromise {
  print("I'm running in the DispatchQueue.global(qos: .background)")
}

you can pass DispatchQueue to run on those queue:

runPromise(on: .main) {
  print("I'm running in the DispatchQueue.main")
}

Chaining Promises

Promise designed to be chainable with other Promise. To chain it, simply call then after each Promise:

runPromise {
  print("I'm running in the DispatchQueue.global(qos: .background)")
}.then {
  print("I'm running on the same DispatchQueue as previous")
}.then(on: .main) {
  print("I'm running in the DispatchQueue.main")
}

You can chain it as much as you need. All of the chaining Promise will be released from the chain after it’s finished doing its task.

You can also pass a value from one Promise to another so it could be used there:

runPromise {
  return "from first promise"
}.then { fromPrevious -> String in
  print(fromPrevious)
  return "from second promise"
}.then(on: .main) { fromPrevious in
  print(fromPrevious)
}

Multiple Thenable

Promise can be handled by multiple Thenable. All you need to do is just call as much Thenable as you need after the particular Promise:

let myPromise = runPromise {
  return Bool.random()
}

myPromise.then { result in
  guard result else { return }
  print("this run when true")
}

myPromise.then { result in
  guard !result else { return }
  print("this run when false")
}

Handling Error

Promise closure is throwable by default. You could always throw an error in the Promise closure to stop next Thenable to be executed

runPromise {
  print("no error here")
}.then {
  throw MyError()
}.then(on: .main) { 
  print("this line will not be executed because previous closure throw an error")
}

You can add error handler closure after then to catch the error and do something with it:

runPromise {
  print("no error here")
}.then {
  throw MyError()
}.handle {
  print($0)
  print("this line will executed with error throwed")
}.then(on: .main) { 
  print("this line will not be executed because previous closure throw an error")
}.handle {
  print($0)
  print("this line will executed with previous error throwed")
}

The error throws from Promise will always passed into all of its child Promise

Finally Block

Promise have finally block which will always be executed regarding error or not the previous Promise is. It will produce another promise which will called after finally is executed:

runPromise {
  print("no error here")
}.then {
  throw MyError()
}.then(on: .main) { 
  print("this line will not be executed because previous closure throw an error")
}.finally { result, error in
  print("this line be executed. Result will be nil and error will be MyError")
}.then {
  print("this line will be executed after finally block finished")
}.finally { result, error in
  print("this line always be executed after all promise is done")
}

Timeout

You can add a timeout to your promise that will automatically throw error if the task is not finished after the given timeout:

runPromise(timeout: 1) {
  doLongTask()
}.then {
  print("task is run for less than 1 second")
}.handle {
  print("task is run for more than 1 second")
}

Droping a promise

Promise can be dropped by calling the drop method. It will then emit an error and skip the current task if not finished yet. You can always pass custom errors when dropping so it will emit that error instead of the default one.

let promise = runPromise {
    print("will be dropped")
}

promise.drop()

Keep in mind that this will only drop the current Promise. finally block and handle block will still be called:

let promise = runPromise {
    print("will not be dropped")
}.then {
    print("will be dropped")
}.handle { error in
    print("will still be executed")
}.finally { result, error in
    print("will still be executed")
}

promise.drop()

Continue with other Promise

You can continue then with new promise. Use thenContinue instead of then, then return a Promise:

runPromise {
    // do something
}.thenContinue {
    return somethingThatReturnAPromise()
}.then {
    print("will executed after promise from somethingThatReturnAPromise() is finished"
}

Combining Promises

You can combine up to 3 Promise to be a single Promise of Tuple as a Result:

let firstPromise = runPromise {
  return "from first Promise"
}
let secondPromise = runPromise {
  return "from second Promise"
}

waitPromises(from: firstPromise, secondPromise).then { result in
  // will print "from first Promise, from second Promise"
  print("\(result.1),\(result.2)")
}

Since waitPromises actually just return back a Promise of Tuple, you can always treat it as regular Promise

Promise status

You can always check the Promise status using its object. its have some properties you can check:

• currentValue which is the latest result from the task, will be nil if the task is not finished yet
• error which is the latest error from the task, will be nil if the task did not emit an error yet
• promiseQueue which is the promise DispatchQueue that run the task
• isCompleted will be true if the task is complete or emitting an error
• isError will be true the task emitting error

let promise = runPromise {
  print("I'm running in the DispatchQueue.global(qos: .background)")
}.then {
  print("I'm running on the same DispatchQueue as previous")
}

print(promise.isCompleted)

New Swift Async

Swift introduce new functionality which is async. Ergo can be used with new async too. To create a Promise from async method, use global asyncAwaitPromise:

asyncAwaitPromise {
  await myAsyncFunction()
}.then { result in
  print(result)
}

In case you want to treat Promise as async, just use result property from Promise:

let asyncResult = try await myPromise.result

It will return the result after finished and throwing error if error is hapens.

You can always convert Task to Promise too:

let promiseFromTask = myTask.asPromise()

or Promise to Task:

let taskFromPromise = myPromise.asTask()

Keep in mind that all of async functionality just available on macOS 10.15, iOS 13.0, watchOS 6.0 and tvOS 13.0

Creating Promise with asynchronous task

Sometimes the task you want to convert to Promise is already an asynchronous task. In this case, you can use asyncPromise instead of runPromise:

asyncPromise(on: .main) { consumer in
  doSomethingAsync { result, error in
    if let error = error {
        consumer.reject(error)
    } else if let result = result {
        consumer.resolve(result)
    }
  }
}.then { result in
  print(result)
}.handle { error in
  print(error)
}

It will emit an error if done param is getting a nil result, or an error other than nil. If the result is not nil, it will run the next Promise task The result of the asyncPromise is Promise, so you can always treat it as a regular Promise

Chain Animation (iOS only)

You can run animation using ChainAnimator which can be chain like Promise:

UIView.chainAnimate(withDuration 0.2)
  .animation {
    view.alpha = 0.5
  }.chain(withDuration: 0.2) {
    view.alpha = 1
  }.animate()

It will run animation from the first one and proceed to the next one after the last one is finished. You can chain as much animation as you need. The result of animate is Promise of Bool. the Bool result will be true if all of the animation is succeed:

UIView.chainAnimate(withDuration 0.2)
  .animation {
    view.alpha = 0.5
  }.chain(withDuration: 0.2) {
    view.alpha = 1
  }.animate()
  .then { succeed in
    print(succeed)
  }

Since the result is regular Promise, you can always treat it as regular Promise

Contribute

You know how, just clone and do pull request