Re: Interfacing to C and types visible to Ada

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Maciej Sobczak wrote:
> Imagine a C API that uses the int type to express something that does
> not have any dedicated domain. In other words, it is not "number of
> apples", not "height in meters", not "hotel room number", etc., it is
> just plain "integer", which meaning can depend on how the given
> library is actually used.

How about making the Ada binding generic, e.g.:

generic
   type Integer_Type is range <>;
package Ada_Binding is
   function Foo return Integer_Type;
end Ada_Binding;

with Interfaces.C;
package body Ada_Binding is
   function Foo return Integer_Type is
      function Internal return Interfaces.C.int;
      pragma Import (C, Internal, "foo");
   begin
      return Integer_Type (Internal);
   end Foo;
end Ada_Binding;

This way, the user of the library specifies the particular meaning of
the "integers" in each case. This design makes it possible to create
several instances of Ada_Binding with different meanings and then
benefit from Ada's strong typing.

--
Ludovic Brenta.