List of packages ?!

List of packages ?!

[Mirko Aigner]

Hello I am a Student and I got the following problem.
I got c++ Code and now I should reimplement it in Ada.
My Problem is: I have a C++ Class only containing methods. In Ada this 
is a package, right ?!
In C++ I can create a list containing this methods-only-class, is that 
possible for ada, too ?!

thanks for the help

Mirko Aigner

Re: List of packages ?!

[Stephen Leake]

Mirko Aigner <Mirko.Aigner@alcatel.de> writes:

> Hello I am a Student and I got the following problem.
> I got c++ Code and now I should reimplement it in Ada.
> My Problem is: I have a C++ Class only containing methods. In Ada this
> is a package, right ?!

Actually, a C++ class corresponds most closely to an Ada tagged type
in a package.

> In C++ I can create a list containing this methods-only-class, is
> that possible for ada, too ?!

Yes. Here is a "null data class with methods":

package Null_Data_Class is

   type Object_Type is tagged null record;

   procedure Method_1 (Object : in Object_Type);

   procedure Method_2 (Object : in Object_Type);

end Null_Data_Class;

There are several list packages for Ada available; see www.adapower.com.

> thanks for the help

You're welcome. 

-- 
-- Stephe

Re: List of packages ?!

[Xavier Nicollin]

Mirko Aigner wrote:
> 
> Hello I am a Student and I got the following problem.
> I got c++ Code and now I should reimplement it in Ada.
> My Problem is: I have a C++ Class only containing methods. In Ada this
> is a package, right ?!

See below.

> In C++ I can create a list containing this methods-only-class,

It's been some time since I last programmed in C++, but I doubt you
can create a list of *class(es)*. I guess you create a list of
*class instances*, that is, a list of objects. So you should do the
same in Ada. Which brings us back to your first question: no, a class
is not a package; a class is a type defined in a package. If it has
only methods, then the record is empty:

package Pack is
   type T is tagged null record; -- could be private
   -- the methods:
   procedure P (X : in T; ...);
   function F (X : T; ...) return ...;
end Pack;

Now, you can create a list of objects of type T, that is, a list
of instances of the class.

Notice that, if your list should contain objects of any "class"
including T and its derivatives, then you need accesses (pointers)
to T'Class (T'Class is the type whose objects are of type T or
of any type derived from T):
   type PT is access all T'Class;
and your list elements are of type PT. I guess this is what you need
(otherwise the list would not be very useful!)

> is that possible for ada, too ?!

Sure, see above.
 
> thanks for the help

You're welcome (in general, and in the Ada world, too).

-- 
| Xavier NICOLLIN (mailto:Xavier.Nicollin@imag.fr) -- INPG (ENSIMAG)
| VERIMAG -- Centre Equation -- 2, ave. de Vignate -- F-38610 Gi�res

Re: List of packages ?!

[Noivet]

I don't know C++ but if this helps you and if it's that what you
search (list of packages) then look here:
http://www.infeig.unige.ch/support/ada/gnatlb/
or http://www.adahome.com/rm95/rm9x-A.html

Re: List of packages ?!

[Mirko Aigner]

Thanks a lot to you Xavier Nicollin, Stephen Leake und Noivet !!

Yes I meant instances of classes!

So I have to define an empty type, and of this empty type I can create 
instances which can be hold in a list. Or the accesses of this type can 
be hold in a list.

thx again !!

Mirko Aigner