ひとつ先読みするeach

gistfile1.rb

module Enumerable
  def each_with_peek_ahead
    @_start = false
    self.each_with_index do |current, idx|
      if idx == 0
        @_last = current
        @_start = true
      else
        yield @_last, current
        @_last = current
      end
    end
    if @_start
      yield @_last, nil
    end
  end
end

def test_ewpa(array)
  puts "test with an Array #{ array.inspect }"
  array.each_with_peek_ahead do |current, ahead|
    puts "current: #{current}, next: #{ahead}"
  end
end

test_ewpa([])
test_ewpa([1])
test_ewpa([1,2])
test_ewpa([1,2,3])
test_ewpa([1,2,3,4])