SafetyDance

A Response Object pattern for resilient Ruby code.

Example:

SafetyDance.new { dance! }.
  then { |result| leave_friends_behind(result) }.
  rescue { |error| not_friends_of_mine(error) }.
  value!

Strongly inspired by John Nunemaker's 'Resilience in Ruby: Handling Failure' post, and the implementation of Github::Result.

Quoting the post:

By putting a response object in between the caller and the call to get the data:

• we always return the same object, avoiding nil and retaining duck typing.
• we now have a place to add more context about the failure if necessary, which we did not have with nil.
• we have a single place to update rescued exceptions if a new one pops up.
• we have a nice place for instrumentation and circuit breakers in the future.
• we avoid needing begin and rescue all over and instead can use conditionals or whatever makes sense.
• we give the caller the ability to handle different failures differently (Conn refused vs Timeout vs Rate limited, etc.).

The key to me including a layer on top that bakes in the resiliency, making it easy for callers to do the right thing in the face of failure. Using response objects can definitely help with that.

Installation

Add this line to your application's Gemfile:

gem 'safety_dance'

And then execute:

$ bundle

Or install it yourself as:

$ gem install safety_dance

Or just copy the relevant code into your project somewhere, such as this minimal implementation:

class Result
  def initialize
    @value = yield
    @error = nil
  rescue => e
    @error = e
  end

  def ok?
    @error.nil?
  end

  def value!
    if ok?
      @value
    else
      raise @error
    end
  end

  def rescue
    return self if ok?
    Result.new { yield(@error) }
  end
end

Usage

Start with passing a block to SafetyDance.new, and continue with the available API.

Instance methods

method call	returns
ok?	true if value when no error else false
value!	value if no error else raises error
error	the rescued error

Instance chain methods

method call	call conditions	yields	returns
then	ok?	return value	instance
rescue	error	rescued error	instance

Development

1. Check out the repo.
2. Run bin/setup to install dependencies.
3. Run rake spec to run the tests.

To install this gem onto your local machine, run bundle exec rake install.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/bf4/safety_dance.

This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

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

Code of Conduct

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