Re: Good/best way to enforce library-level instantiation a generic package

["Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>]

On 3/17/20 2:21 AM, Randy Brukardt wrote:
> "Vincent Marciante" <vincent.marciante@l3harris.com> wrote in message
> news:6bcc6133-8c8b-4252-a8e6-fd64a5eec2ca@googlegroups.com...
>> I made a generic package that I want only to be instantiated at library
>> level.
>> I'm working on compile-time a way to enforce that desire which involves
>> access
>> type accessibility level checking but have not yet set it up correctly.
>> Is there a better/standard way?
> 
> For Ada 95, deriving from Controlled does the trick, but that was eliminated
> (at substantial cost) in Ada 2005 and later.
> 
> I suppose you could use type String_Access (which is a library-level access
> type) for this:
> 
>     with Ada.Strings.Unbounded;
>     generic
>         ...
>     package My_Generic is
>         -- Real stuff here.
> 
>         Library-Level : constant aliased String := "Library-Level";
>         Check : Ada.Strings.Unbounded.String_Access := Library_Level'Access;
>              -- 'Access is illegal if My_Generic is not instantiated at the
> library level.
>     end My_Generic;

Check should be constant, too.

For the OP:

You can also use Ada.Tags.Expanded_Name on a tagged type declared in the generic:

type T is abstract tagged null record;
Name : constant String := Ada.Tags.Expanded_Name (T);
pragma Assert
    (Ada.Strings.Fixed.Index (Name (Name'First .. Name'Last - 2), ".") = 0,
     "Generic_Name must be instantiated at library level");

-- 
Jeff Carter
"Gentlemen, you can't fight in here. This is the War Room!"
Dr. Strangelove
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