Map a series of methods successively, plus extra goodies

map_chain.rb

require 'blankslate'

# Instead of writing
#
#     > (1..3).map(&:even?).map(&:to_s).map(&:upcase).map(&:reverse)
#      => ["ESLAF", "EURT", "ESLAF"] 
#
# write the more concise
#
#     > (1..3).map_chain.even?.to_s.upcase.reverse.result
#      => ["ESLAF", "EURT", "ESLAF"] 
#
# 
# You can pass arguments to methods in the chain:
#
#     > (1..3).map_chain.*(2).even?.result
#      => [true, true, true]
#
# or call arbitrary blocks using _:
#
#     > (1..3).map_chain._{|i| i * 2 + 1 }.even?.result
#      => [false, false, false]
#
#
# Reuse intermediate results as you'd expect:
#
#     > caps = %(foo bar baz).map_chain.upcase
#     > caps.result
#      => ["FOO", "BAR", "BAZ"]
#     > twicecaps = caps._{|str| str * 2 }
#     > twicecaps.length.result
#      => [6, 6, 6]
#     > caps.result
#      => ["FOO", "BAR", "BAZ"]
#
#
# Error messages are still helpful in case of typos:
#
#     > (1..3).map_chain.even?.non_existent_method
#     NoMethodError: undefined method `non_existent_method' for false:FalseClass

module Enumerable
  def map_chain
    MapChain.new(self)
  end
end


class MapChain < BlankSlate
  def initialize(receiver); @mappable = receiver; end

  def method_missing(sym, *args, &block)
    MapChain.new(@mappable.map {|o| o.__send__(sym, *args, &block) })
  end

  def respond_to?(method)
    @mappable.empty? || @mappable.first.respond_to?(method)
  end

  def _(&block)
    yield self
  end

  def result
    @mappable
  end
end