theblixguy / taskbuilder

Experimental DSL for creating async tasks using Swift 5.1 Function Builders

TaskBuilder

TaskBuilder is an experimental DSL for performing async tasks (using OperationQueue), powered by the new function builders feature in Swift 5.1.

Example

func createImageTask(_ completion: @escaping (Data) -> Void) -> Task {
  Do {
    Action { print("Starting...") }

    LoadBigImageTask()
    Action { print("Load big image task finished!") }

    Passthrough(task: VeryBigImageTask()) { task in
      Action { completion(task.imageData) }
    }

    Action { print("All done!") }
  }
}

let queue = OperationQueue()
let task = createImageTask { print($0) }
queue.addTask(task)

Basics

TaskBuilder allows you to define tasks sequentially, rather than executing them at any order. This simply means that order in which you define the tasks is the order in which they are executed.

TaskBuilder comes with a very simple protocol, called Task. A Task has two requirements - a perform() method and completionBlock property (which is simply () -> Void).

TaskBuilder also provides a default implementation of Task on Operation so you can easily start using your existing operation classes.

Built-in tasks

Do

A Do task is a top level task that encapsulates child tasks. Your task must always start with a Do at the top level.

Action

An Action task is used to perform any kind of simple action (that does not return). For example - calling print(...), calling a completion handler, etc.

Passthrough

A Passthrough is a special kind of task, that takes a Task as input and then provides that same task in a completion block once that task has finished executing. This allows you to access the properties and methods on that task once its completed.

For example - this can be useful when you want to pass the downloaded data to a completion handler.

Limitations

This is an experimental package and is very basic in terms of functionality. For example - you cannot just create any kind of ordering you want, like putting another Do inside a Passthrough or an Action inside another.

This is simply a way for me to experiment with this new feature. I made this in a few hours, so don't be harsh 😄 I will be improving this with time, so stay tuned.

PRs are welcome if you want to contribute something!