--- delete_if {|x| ... }
--- reject! {|x| ... }

    Ǥ֤˥֥åϤɾη̤ˤʤäǤ
    ٤ƺޤ

    delete_if Ͼ self ֤ޤreject! 
    Ǥ 1 Ĥʤ nil ֤ޤ

