Re: OO Style with Ada Containers

[Matthew Heaney <matthewjheaney@earthlink.net>]

braver <deliverable@gmail.com> writes:

>>    type Scanner (<>) is tagged limited private;
>
> What does (<>) say here -- that the type is unconstrained?

Yes, this forces the type to have an initialization expression.  Here the type
is also limited, so that means must call one of the primitive operations
(loosely the "constructor" functions) that returns type Scanner; the only one I
defined in the example was operation Scan.

This is all a bit of a trick, since it allows me to put the storage for the
current line on the stack:

declare
  S : Scanner := Scan (Get_Line (F));
begin


> What's the logic behind the definition and usage of the Handle H
> throughout?

This is known as the "Rosen Trick".  It allows a function to modify its
argument (which you normally cannot do in Ada, since it doesn't allow in out
mode for function parameters).

Here I want function Word to return the current token on the line, and then
consume that token and advance to the next one.  You don't have to do it that
way, since you could always make the Next operation public.