simple runner for before/after each/all tasks

runner.rb

# Sometimes you want to run a set of blocks before/after
# each/all of something. Problem solved.
#
# @example
#   
#   class CountDown < Runner
#     before :all do |arr|
#       arr.collect {|i| i + 1 }
#     end
#     
#     before :all do |arr|
#       arr.reverse
#     end
#     
#     before :each do |n|
#       print "in "
#     end
#     
#     after :each do |n|
#       print n.to_s + "!\n"
#     end
#     
#     after :all do
#       puts "LIFT OFF!"
#     end
#     
#     def self.from(n)
#       numbers = (0...n).to_a
#       numbers = run(:before, :all, numbers)
#       
#       numbers.collect! do |n|
#         run :before, :each, n
#         run :after, :each, n
#       end
#       
#       run :after, :all
#     end
#   end
#   
#   CountDown.from(5)
#   #=> in 5!
#   #=> in 4!
#   #=> in 3!
#   #=> in 2!
#   #=> in 1!
#   #=> LIFT OFF!
#
class Runner

  # In "real life" you probably wouldn't be able to use the
  # new 1.9 syntax, but it is nicer.
  @@blocks = {
    before: {
      all: [],
      each: []
    },
    after: {
      all: [],
      each: []
    }
  }
  
  # @example
  #
  #   before :all do |arg|
  #     p arg
  #   end
  #
  def self.before(a, &block)
    @@blocks[:before][a] << block
  end
  
  # @example
  #
  #   after :each do
  #     p "bye"
  #   end
  #
  def self.after(a, &block)
    @@blocks[:after][a] << block
  end
  
  # Call each block in turn, use with common sense. 
  # Passes +args+ to the first block that is run, in order
  # that they were defined, then passes result of that to
  # the next block and so on.
  #
  # @example
  #
  #   def read_all(files)
  #     files = run :before, :all, files
  #     
  #     files.collect! do |file|
  #       file = run :before, :each, file
  #       # do something to +file+
  #       run :after, :each, file
  #     end
  #     
  #     files = run :after, :all, files
  #   end
  #
  # @return 
  #   Result of the last executed block.
  #
  def self.run(time, a, *args)
    r = nil
    @@blocks[time][a].each do |b|
      if r
        r = b.call(r)
      else
        r = b.call(*args)
      end
    end
    r
  end
  
  # def run(time, a, *args); self.class.run(time, a, *args); end
  
end