AI-344, generics/instances...

["Martin Dowie" <martin.dowie@baesystems.com>]

Just a thought that popped into my head and I wanted a 'sanity' check on if
first...

With AI-344 generic packages that define a tagged type no longer have to be
instantiated at library level. I was wondering if it would be useful to
define a mechanism (pragma?) that allowed an author to insist that a generic
package be instantiated at library level.

This came to me when I was looking at my Singleton pattern, which is just
fine for Ada95 but will be much more open to abuse come Ada0Y. My code looks
roughly like this:

  generic
  package Patterns.Generic_Singletons is
     type Singleton is tagged private;
  private
     -- Implementation that uses assumes library level instance
  end Patterns.Generic_Singletons;

Perhaps something as simple as:

  generic
  package Patterns.Generic_Singletons is
     pragma Library_Level_Unit; -- new pragma
     type Singleton is tagged private;
  private
     -- Implementation that uses assumes library level instance
  end Patterns.Generic_Singletons;

Our am I missing something?

Cheers
-- Martin