correction to my reply.

> this is just one of what i had been seeking in vain for !!

while i was in my regeneration cycle, i found that this is not the ideal
behavior for me.

> > irb(main):003:0> require 'enumerator' 
> > => true
> > irb(main):004:0> [1,2,3,4,5,6].each_cons(2) {|x| p x }
> > [1, 2]
> > [2, 3]
> > [3, 4]
> > [4, 5]
> > [5, 6]
> > => nil
> > irb(main):005:0> [1,2,3,4,5,6].each_cons(3) {|x| p x }
> > [1, 2, 3]
> > [2, 3, 4]
> > [3, 4, 5]
> > [4, 5, 6]

what i am expecting is as below.

  [1,2,3.4.5.6].sliding_each(2) {|x| p x}
  [nil,1]
  [1,2]
  [2,3]
  [3,4]
  [4,5]
  [5,6]
  [6,nil]

on the other hand, it is easy by like this.

  [ nil, enumeratee, nil ].flatten.each_cons(2) { |x| p x }

q2hdp://void/3d/universe/milky-way-galaxy/orion-arm/sol-solar-system/
3rd-planet/fareast/jp/tky/shigetomi.takuhiko.5618