Godefer

Godefer implements the defer / recover mechanism from Go. It allows grouping operations together that require a closing of some sort after opening. I don't really know the usefulness of this gem, though I will take issues and pull requests.

Installation

Add this line to your application's Gemfile:

gem 'godefer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install godefer

Usage

Godefer allows two different uses. The first using a general block, which would mostly be useful probably writing one off scripts of some sort. The other is to include the Defer module into your own class and running code within a with_defer block.

Block Usage

Example of writing to an output file. The defer {} block gets called at the end of the run block.

Defer.run do
  f = File.open('output.log')
  defer { f.close }

  # do stuff that uses f
end

Deferred blocks are handled in a LIFO ordering, to ensure any operations work their way back up to ensure any dependencies are closed out properly.

Defer.run do
  puts "opening"
  defer { puts "closing" }
  puts "start filter"
  defer { puts "stop filter" }
  # ...
end

# Output:
#   opening
#   start filter
#   stop filter
#   closing

Module Usage

Similar example where we are doing a bunch of stuff within a class.

class Audit
  include Defer
  attr_accessor :file

  def large_operation
    with_defer do
      opening
      defer { closing }

      helper
      # ...
    end
  end

  def opening ; "..." ; end
  def helper  ; "..." ; end
  def closing ; "..." ; end
end

Recovering Exceptions

Exceptions raised can be recovered within a deferred block. If an exception is recovered within a defer block, the exception is stopped. If an exception is raised, and recover is not called in a deferred method the exception will be raised from the Defer.run or with_defer block. All Deferred blocks reached get called regardless of an exception being raised or not.

Defer.run do
  defer do
    if ex = recover
      puts "We stopped an exception: #{ex}"
    end
  end

  raise StandardError.new("Important Message")
end
# Output:
#   We stopped an exception: Important Message

Defer.run do
  defer { puts "see" }
  raise StandardError.new("Error")
end
# Output:
#   see
#
# => StandardError: Error
# => from (pry):3:in `block in __pry__'

Development

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

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

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