APromise

A simple Promise implementation for Ruby Async. This is level-triggered, meaning APromise#wait will wait if necessary, or return the previous resolution value if one has already been supplied.

Add this line to your application's Gemfile:

gem 'apromise'

And then execute:

bundle install

Or install it yourself as:

gem install apromise

Within any Async reactor:

Async do
  promise = APromise.new

  Async do
    value = promise.wait
  end

  promise.resolve(value: :example)
end

It's intended that resolve be called once and once only. Calling it more than once may lead to unpredicable behavior.

The resolution value can be determined via a block as well:

Async do
  promise = APromise.new

  Async do
    value = promise.wait
  end

  promise.resolve do
    :example
  end
end

This form makes it easier to capture and propagate any potential exceptions.

Note that the .wait call does not have to be established prior to the promise being resolved. It can be called any time:

Async do
  promise = APromise.new

  promise.resolve(value: :example)

  Async do
    value = promise.wait
  end
end

In this case calling wait returns the value immediately.

It's also possible to create a promise that comes pre-resolved as this might prove useful in situations where the response from a call must be a promise:

Async do
  promise = APromise.new(value: :example)

  Async do
    value = promise.wait
  end
end

In this case no actual waiting is performed, the value is just returned.

The new method also takes a block like resolve and will capture and re-raise exceptions accordingly.

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

Bug reports and pull requests are welcome on GitHub at https://github.com/postageapp/apromise. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the Apromise project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.