--- fetch(nth)                          ruby 1.7 feature
--- fetch(nth, ifnone)                  ruby 1.7 feature
--- fetch(nth) {|nth| ... }             ruby 1.7 feature

    Array#[nth] [Array/[]] Ʊ nth ܤǤ֤ޤ
    Array#[nth] Ȥ nth ܤǤ¸ߤʤο񤤤
    ʤޤ

    ǽηǤϡ㳰 IndexError ȯޤ
    ܤηǤϡ ifnone ֤ޤ
    ܤηǤϡ֥åɾ̤֤ޤ

    Array#[nth] ϡArray#fetch(nth, nil) ƱǤ

