guideline

Use the package Interfaces and its language-defined child packages rather than implementation-specific mechanisms.

Consider using pragma Import rather than access-to-subprogram types for interfacing to subprograms in other languages.

Isolate all subprograms employing pragmas Import, Export, and Convention to implementation-specific (interface) package bodies.

This example shows how to interface with the following cube root function written in C:

double cbrt (double x);
------------------------------------------------------------------------------

package Math_Utilities is

   Argument_Error : exception;

   function Cube_Root (X : Float) return Float;

   ...

end Math_Utilities;
   
------------------------------------------------------------------------------
with Interfaces.C;
package body Math_Utilities is

   function Cube_Root (X : Float) return Float is

      function C_Cbrt (X : Interfaces.C.Double) return Interfaces.C.Double;
      pragma Import (Convention    => C,
                     Entity        => C_Cbrt,
                     External_Name => "cbrt");

   begin
      if X < 0.0 then
         raise Argument_Error;
      else
         return Float (C_Cbrt (Interfaces.C.Double (X)));
      end if;
   end Cube_Root;

   ...

end Math_Utilities;

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