Question

I would like to declare some “user-defined compiler-constants” to keep my specification files as “constant” as possible. This is something common in C++, e.g. :

// misc/config.hh
namespace misc
{
  typedef std::shared_ptr<A> A_ptr; 
  namespace arch = ibmpc;
}

// misc/code.hh
#include "misc/config.hh"
namespace misc
{
  void function p(A_ptr a);
}

Which would be in Ada :

-- misc.ads
package Misc is
  use Types; ----> forbidden !

  procedure P(A : A_Access);
end Misc;

-- misc-types.ads
package Misc.Types is
  type A_Access is A'Access;
end Misc.Types;

Of course this does not work since use is a context keyword…hence my question : how is it possible to do something with the same results in Ada ?

Answer 1

I think this is a reasonable mapping from your C++ original to Ada:

To start with, corresponding more-or-less, I think, to your namespace misc, in file misc.ads,

package Misc is
end Misc;

Then, corresponding to config.hh, in file misc-config.ads,

package Misc.Config is
   type A is (For_Example, An_Enumeration);
   type A_Access is access A;
end Misc.Config;

(which could, of course, also reference types in Misc). Then, corresponding to code.hh, in file misc-code.ads,

with Misc.Config;
package Misc.Code is
   use Config;
   procedure P (A : A_Access);
end Misc.Code;

Personally I wouldn’t use Config;, at any rate in specs – it can make it difficult to work out where something is defined. Note, you can say use Config; or use Misc.Config; where shown, because you’re in a child of Misc; in the context clause, which is also OK, you would have to use Misc.Config;.