--- delete_at(pos)

    pos ǻꤵ줿֤ˤǤ֤ޤ
    pos ϰϳǤä nil ֤ޤ

    at ƱͤΥǥå֤ꤹ뤳
    ȤǤޤ

    :

        array = [0, 1, 2, 3, 4]
        array.delete_at 2
        p array             #=> [0, 1, 3, 4]

