Eventkit::Promise

Promises/A+ for Ruby

Supported Ruby versions: 1.9.3, 2.0, 2.1, 2.2

Installation

Add this line to your application's Gemfile:

gem 'eventkit-promise'

Configuration

On fullfiled and on rejected handlers should execute asynchronously according to the [Promises\A+ spec] (https://promisesaplus.com/#point-67). So, the main dependency for an Eventkit::Promise is the object that provides the execution context for handlers, which we will be calling the TaskScheduler.

In your project, you will need to define an implementation for a TaskScheduler, which sould have a #schedule_execution method that takes a block.

If you're using something like Event Machine, then you could do something like this:

require 'eventkit/task_scheduler'

class EMTaskScheduler < EventKit::TaskScheduler
  def schedule_execution(&block)
    EM::next_tick(&block)
  end
end

task_scheduler = EMTaskScheduler.new

Eventkit::Promise.new(task_scheduler)

If you're using Eventkit::Eventloop, then you could do:

require 'eventkit/task_scheduler'

class NextTickScheduler < Eventkit::TaskScheduler
  def initialize(event_loop)
    @event_loop = event_loop
  end

  def schedule_execution(&block)
    @event_loop.on_next_tick(&block)
  end
end

task_scheduler = NextTickScheduler.new

Eventkit::Promise.new(task_scheduler)

Usage

require 'eventkit/promise'

# Resolving a promise

promise = Eventkit::Promise.new(task_scheduler)

promise.then(->(value) { value + 1 })

promise.resolve(1)

# Rejecting a promise

promise = Eventkit::Promise.new(task_scheduler)

promise.then(
  ->(value) {
    value + 1
  },
  ->(error) {
    log(error.message)
  }
)

promise.reject(NoMethodError.new('Undefined method #call'))

# Chaining promises

promise_a = Eventkit::Promise.new(task_scheduler)

promise_b = promise_a
  .then(->(v) { v + 1 })
  .then(->(v) { v + 1 })
  .then(->(v) { v + 1 })

promise_b.catch { |error|
# Handle errors raised by any of the previous handlers
}

promise_a.resolve(1)

# Resolving and fullfiling with another promise

promise_a = Eventkit::Promise.new(task_scheduler)
promise_b = Eventkit::Promise.new(task_scheduler)

promise_a.resolve(promise_b)

promise_b.resolve('foobar')

# Resolving and rejecting with another promise

promise_a = Eventkit::Promise.new(task_scheduler)
promise_b = Eventkit::Promise.new(task_scheduler)

promise_a.resolve(promise_b)

promise_b.reject('Ooops can not continue')

# Initializing with a block

promise = Promise.new(task_scheduler) do |p|
  p.resolve('foobar')
end

Contributing

1. Fork it ( https://github.com/[my-github-username]/eventkit-promise/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request
6. Happy hacking!