Re: Usage of Interfaces with Ada 95

[Matthew Heaney <matthewjheaney@earthlink.net>]

Simon Wright <simon@pushface.org> writes:

> The STL means something quite like "designator of one end of a
> half-open range".
> 
> I am not a C++ speaker, but
> 
>   for (i = cont.start(); i != cont.oneAfterTheEnd(); i++)
> 
> is *not* the way the GoF, or Grady, describe it.

I disagree that this is any different.  Let's rewrite the generic
algorithm that I posted earlier, to use Simon's preferred syntax:

   generic
      type IT is private;
      with function Succ (I : IT) return IT is <>;
      with procedure Process (I : IT) is <>;
      with function Is_Done (I : IT) return Boolean is <>;
   procedure Generic_Algorithm (First : in IT);

Now let's use the a Charles list (say) to instantiate the Simon
algorithm:

   procedure Op (List : in List_Subtype) is

      procedure Process (I : IT) is ...;

      function Is_Done (I : IT) return Boolean is
      begin
         return I /= Back (List);
      end;

      procedure Algorithm is
        new Generic_Algorithm (IT, Succ, Process, Is_Done);
   begin
      Algorithm (First (List));
   end;

It's equivalent to what I showed yesterday.  There is no difference
between "STL" iterator and "Booch" iterator, except for syntax.

In fact you could easily convert Grady's active iterator implementation
of p. 158 to use Stepanov syntax, by simply declaring a constant of type
Iterator (equal to null internally) and providing an equality operator
for Iterator.

It's all the same.