Re: Full view of a private partial view cannot be a subtype

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

On 2017-12-19 02:01, Jere wrote:
> On Sunday, December 17, 2017 at 10:39:17 AM UTC-5, Dmitry A. Kazakov wrote:
>> On 2017-12-17 16:26, Jere wrote:
>>
> Something like:
> 
> generic
>     type Item_Type(<>);
>     type Item_Access is access Item_type;
>     with procedure Deallocation(Ref : in out Item_Access);
> package Sledgehammer is
>     <types>
>     <operations>
> private
>     <implementation>
> end Sledgehammer;
> 
> This would be used in maybe 5% or less of the code base and only
> when absolutely necessary.  I want to convert it to:
> 
> generic
>     type Item_Type(<>) is limited private;
> package Nicer_Package is
>     type Item_Access is access Item_Type;
>     <same types>
>     <same operations>
> private
>     procedure Deallocate is new Ada.Unchecked_Deallocation
>        (Item_Type,Item_Access);
> 
>     package Implementation is new Sledgehammer
>        (Item_Type => Item_Type,
>         Item_Access => Item_Access,
>         Deallocation => Deallocate);
> 
>     <implementation>
> end Nicer_Package;
> 
> Since all I am doing is automating the access type and
> the deallocation operation, I don't think a new type
> is really the right design. Additionally, I don't want
> to expose the deallocation operation as it should never
> be called directly.

How do you create objects?

There are two approaches:

1. Explicit new, implicit deallocate. This works only with containers, 
which should know the access type and the deallocator.

2. Factory (a Create call), implicit deallocate. This requires reference 
counting or custom GC pool.

P.S., declaring an access type in the public part of a generic is 
suspicious for bad design.

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