X'Last, where X is any scalar type (for example integer, enumerated, real), is an attribute that represents the last value (upper bound) in the range of type X. The value returned is of type X.
type My_Enum is (Enum1, Enum2, Enum3);
type My_Int is range -1 .. 5;
pragma Assert (My_Enum'Last = Enum3); -- OK
pragma Assert (My_Int'Last = 5); -- OK
pragma Assert (My_Int'Last = 4); -- Wrong!