Re: Re-exporting primitive operations of a private type (like "-", and 'min)

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Mon, 31 Oct 2005 10:27:51 +0200, Niklas Holsti wrote:

> Anonymous Coward wrote:
>>>The whole point of private types is that the only visible operations
>>>on them are assignment, equality and inequality, and any explicitly
>>>defined operations in the visible part of the package
>>>specification. 
>> 
>> That makes sense.  As a default, it probably would be a poor language
>> design to have private types automatically export public primitive
>> operations.  If I created an Altitude_Type, I wouldn't want to inherit
>> the "+" operation.
> 
> The following is perhaps not quite on the original topic, but this 
> thread reminds me of an idea for a new feature related to private 
> types that I would like to present.
> 
> My Ada packages often define types that are *mostly* private in 
> the sense that I only want the clients to use a restricted set of 
> operations and properties of the type. However, I often do not 
> make these types actual private types because I want to reveal 
> some properties, such as discreteness, that I cannot now specify 
> for a private type.
> 
> I would like to be able to reveal some properties of private types 
> in the same way as we can now define generic formal types, for 
> example saying that the type is discrete (type T is (<>)) or is a 
> modular type (type T is mod <>).

[...]

> Does this idea appeal to anyone?

That would a repetition of the error made with generics. Instead of

   type Element is private (<>);

it should be just

   type Element is new Abstract_Integer with private;

which would solve everything.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de