RE: Extensible Enummerated types FW: When will next Ada revision be? (83, 95, ?)

["Robert C. Leif, Ph.D." <rleif@rleif.com>]

From: Bob Leif
To: Ted Dennison et al.

There actually is a class 'tag in the program. Unfortunately, it does NOT
solve the problem.
----------------------------------------
with Ada.Text_Io;
generic
   type Enum_Type is (<>);
   type Info_Type is private;
package Generic_Rec_W_Enum_Part_Pkg is
   type Enum_Rec_Type is tagged record
      Enum_Part : Enum_Type;
      Info_Part : Info_Type;
   end record;

--This is instantiated

type Prefix_Type is (None, Mr, Ms, Miss, Mrs, Dr, Prof, Rev,
    Other);

package Prefix_Recs is new Generic_Rec_W_Enum_Part_Pkg
    (Enum_Type => Prefix_Type,
    Info_Type => Prefix_Bd_Type); --15 character bounded_string.

subtype Prefix_Rec_Type is Prefix_Recs.Enum_Rec_Type;

None_Rec : constant Prefix_Rec_Type := (None, Null_Prefix_Suffix_Bd);
  Mr_Rec   : constant Prefix_Rec_Type := (Mr,To_Bd("Mr."));
  Ms_Rec   : constant Prefix_Rec_Type := (Ms,To_Bd("Ms."));
  Miss_Rec : constant Prefix_Rec_Type := (Miss,To_Bd("Miss"));
  Mrs_Rec  : constant Prefix_Rec_Type := (Mrs,To_Bd("Mrs."));
  Dr_Rec   : constant Prefix_Rec_Type := (Dr,To_Bd("Dr."));
  Prof_Rec : constant Prefix_Rec_Type := (Prof,To_Bd("Prof."));
  Rev_Rec  : constant Prefix_Rec_Type := (Rev,To_Bd("Rev."));
  Other_Rec : Prefix_Rec_Type := (Enum_Part => Other,
    Info_Part => To_Bd("Other"));

The addition of a new type (field) to Prefix_Rec_Type does not permit
addition of new objects of Prefix_Rec_Type; because, Prefix_Rec_Type is
limited by the number of items in the enumerated type Prefix_Type.

The only obvious way to solve this problem is to permit the extension of
Prefix_Type by the addition of new enumerated values. I had to circumvent
the enumeration by including "Other". The use of Other significantly
decreases the capacity of monitoring membership in the set of an enumerated
type. Although my suggestion will require effort on the part of compiler
vendors, I believe that it will aid the programmers.

-----Original Message-----
From: comp.lang.ada-admin@ada.eu.org
[mailto:comp.lang.ada-admin@ada.eu.org]On Behalf Of Ted Dennison
Sent: Monday, January 22, 2001 7:02 AM
To: comp.lang.ada@ada.eu.org
Subject: Re: Extensible Enummerated types FW: When will next Ada
revision be? (83, 95, ?)


In article <mailman.979975693.13263.comp.lang.ada@ada.eu.org>,
  comp.lang.ada@ada.eu.org wrote:
> I believe that at one time you mentioned the possibility of extending
> an enumerated type. This would greatly facilitate object oriented
> programming. For instance, I have created a Person_Names package. The

Why can't you use the class' tag for that purpose?

--
T.E.D.

http://www.telepath.com/~dennison/Ted/TED.html


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