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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: List container strawman 1.1
Date: 11 Nov 2001 21:09:04 +0000
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Date: 2001-11-11T21:09:04+00:00
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Jeffrey Carter <jrcarter@acm.org> writes:

> Ted Dennison wrote:
> > 
> > Generally, I'd agree with you. However, at least one person did use the
> > word "unaceptable" when I described the multi-level instantiation
> > process a Booch user has to go through.
> 
> I think I used "unacceptable" to refer to the several hours of study
> you said was necessary to learn to instantiate a simple data
> structure.  Multiple instantiations are undesirable, but multiple
> instantiations that take hours to learn to use unacceptable.

I think it only takes hours the first time (and without any help).


>From the documentation:

In the example, a Car has three attributes, the Plate (the Index Mark;
my first car's was 8493KC), the Model name (it was a Vauxhall Cresta)
and the date it was Registered (some time in the mists of antiquity).

   with Ada.Calendar;
   with Ada.Strings.Bounded;
   package Cars is

      package Plate_Strings
      is new Ada.Strings.Bounded.Generic_Bounded_Length (10);
      subtype Plate_String
      is Plate_Strings.Bounded_String;

      package Model_Strings
      is new Ada.Strings.Bounded.Generic_Bounded_Length (32);
      subtype Model_String
      is Model_Strings.Bounded_String;

      type Car is record
         Plate : Plate_String;
         Model : Model_String;
         Registered : Ada.Calendar.Time;
      end record;

   end Cars;

A company's Fleet holds a number of Cars. 

The first thing to do is to instantiate the top-level abstract
Containers for Car. Note, we have to supply an equality operator ("=")
for Car; we could also just use Cars.

   with BC.Containers;
   with Cars;
   package Abstract_Car_Containers
   is new BC.Containers (Cars.Car, "=" => Cars."=");

Next, using the new Abstract_Car_Containers, instantiate the abstract
Collections:

   with Abstract_Car_Containers;
   with BC.Containers.Collections;
   package Abstract_Car_Collections
   is new Abstract_Car_Containers.Collections;

You now have to choose the representation to be used for the concrete
Collection. To start with, assume that you'll never have more than 30
Cars to deal with. This means that you can use the Bounded form.

   with Abstract_Car_Collections;
   with BC.Containers.Collections.Bounded;
   package Fleets
   is new Abstract_Car_Collections.Bounded (Maximum_Size => 30);

You now need to create your Fleet: 

   with Fleets;
   package My_Fleet is

      The_Fleet : Fleets.Collection;

   end My_Fleet;




There, not so bad eh :-)