/* * call-seq: * dvector.at(int) -> number or nil * * Returns the element at index _int_. A * negative index counts from the end of _dvector_. Returns +nil+ * if the index is out of range. * * a = Dvector[ 1, 2, 3, 4, 5 ] * a.at(0) -> 1 * a.at(-1) -> 5 */ VALUE dvector_at(VALUE ary, VALUE pos) {