async.rb

require 'async'

class Enumerator
  class Async
    module Refinement
      refine Enumerable do
        def async
          Enumerator::Async.new(self)
        end
      end
    end

    include Enumerable

    def initialize(collection)
      @enum = collection.to_enum
    end

    def eager
      return @enum unless @enum.respond_to?(:eager)

      @enum.eager
    end

    def lazy
      @enum.lazy
    end

    def async
      self
    end

    def each(&block)
      Sync do |task|
        @enum.each do |value|
          task.async do
            block.call(value)
          end
        end
      end

      self
    end
  end
end

using Enumerator::Async::Refinement

[1, 2, 3].async.map do |number|
  sleep 2
  number + 42
end

Async creates a new task if it runs within an existing reactor. So I would maybe change line 34 to Sync do |task|:

• It will start a new reactor (just like top-level Async) if one doesn't yet exist
• If the method runs inside an existing reactor (Async block) it will just run synchronously

@bruno- that makes sense and is really interesting. I hadn't thought of it being used inside an existing reactor. Thank you for your feedback! I updated the gist accordingly to use Sync.