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From: Ted Dennison <dennison@telepath.com>
Subject: Re: packet type ?
Date: 2000/01/18
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 <38845EBD.6F90845D@icn.siemens.de>
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In article <38845EBD.6F90845D@icn.siemens.de>,
  Alfred Hilscher <Alfred.Hilscher@icn.siemens.de> wrote:
>
> Ted Dennison wrote:
> I think thats not quite the same. Taking the example below, how would
> you do this with generics ?
>
> package type stack is
>   push (item : in ...);
>   pop  (item : out ...)
> end stack
>
> procedure application is
>   User_stack : stack;
>   Supervisor_stack : stack;
>   Interrupt_stack : stack;
>
>   Any_Stack : access Stack;
> begin
>  ...
>   Any_Stack := new Stack; -- how do this  ???
>  ...
> end application;

The flip answer is I'd download the Booch components. :-)

Code wise, I'd do something like this:

generic
   type Element is private;
package Stack is
   type Instance is private;

   Push (Item : in Element
         Onto : in out Instance);
   Pop  (Item   :    out Element;
         Off_Of : in out Instance);
private
...
end Stack;

It looks like your confusion is based on experience w/ other OO-based
languages. In Ada types and packages are completely separate kinds of
entities. Packages exist to provide for organizing other things into a
single namespace. Types define the data structure of objects.
Subprograms are defined within the context of packages, not types or
objects. For instance, to call what I created above, first I'd
instantiate it with my element type thusly:
   with Stack;
   ...
   procedure Whatever is
      package Integer_Stack is new Stack (Integer);

Then I call push this way:
      Pushee : Integer := 20;
      Old_Integers : Integer_Stack.Instance;
      ...
   begin
      Integer_Stack.Push (Item => Pushee,
                          Onto => Old_Integers);

--
T.E.D.

http://www.telepath.com/~dennison/Ted/TED.html


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