Re: Package instantiation and automatic de-allocation.

[tmoran@acm.org]

> Your package below does not work because it lacks a public
> declaration for your Stack type. Once you have a name for the
> type you must pass an instance of that type to each function and
> procedure. Ada does not have an impicit "this" variable like C++ or
> Java.
  That's true if you want to allow multiple Stack objects, perhaps
arrays of Stacks, etc.  Sometimes you really only want one or very
few objects, so one/generic instantiation is good.  For instance,
say you have a space rocket with two similar radios, one of which
talks to Earth and the other to your Moon base.  You might then
   generic
     Hardware_Port : Natural;
   package Communications is ...
     procedure Send(...);
     procedure Receive(...);
 ...
 package Earth is new Communications(Port=>16#378#);
 package Moon is new Communications(Port=>16#278#);

Then you can say
  Earth.Send(...);
  Moon.Receive(...);
But if you had 4 moon bases, you would have to
  package Moon_1 is new Communications(...
  package Moon_2 is new Communications(...
  package Moon_3 is new Communications(...
  package Moon_4 is new Communications(...
you couldn't make an array Moon(1 .. 4).

> without having to dick with Unchecked_Deallocation.
If you never say "X := new ...", you never have to use
Unchecked_Deallocation.  If you declare an object or do a generic
instantiation in a declare, it will automagically be deallocated
when you leave that scope.