Re: Supertypes RE: Extensible Enumerated types

[Jeffrey Carter <jrcarter@acm.org>]

"Beard, Frank" wrote:
> I like Jeff Creem's idea of:
> 
> type Fruit_Type is (Apple, Orange);
> type New_Fruit_Type is new Fruit_Type with (Pear, Kiwi);

This seems like an excellent idea. The only difference between this and

type New_Fruit_Type is (Apple, Orange, Pear, Kiwi);

would be type conversions between the types:

F : Fruit_Type     := ...;
N : New_Fruit_Type := ...;

N := New_Fruit_Type (F); -- Always OK
F := Fruit_Type (N);     -- Raises Constraint_Error if N not in
                         -- Apple .. Orange

Are there any technical/implementation issues against this?

-- 
Jeff Carter
"We call your door-opening request a silly thing."
Monty Python & the Holy Grail