--- last
--- last(n)    ruby 1.8 feature

    Ǥ֤ޤ󤬶ΤȤ nil ֤ޤ

        p [0, 1, 2].last   #=> 2
        p [].last          #=> nil

    ruby 1.8 feature:
    άǽʰ n ꤷ硢 n Ǥ
    ֤ޤn  0 ʾǤʤФʤޤ

        ary =  [0, 1, 2]
        p ary.last(0)
        p ary.last(1)
        p ary.last(2)
        p ary.last(3)
        p ary.last(4)
        # => []
             [2]
             [1, 2]
             [0, 1, 2]
             [0, 1, 2]

    Array#first [Array/first] ⻲ȤƤ

