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From: Stephen Leake <Stephen.Leake@gsfc.nasa.gov>
Subject: Re: Please Help.
Date: 1997/09/15
Message-ID: <341D4041.4AF8@gsfc.nasa.gov>#1/1
X-Deja-AN: 272652956
References: <01bcbcde$f8a425c0$ca70fe8c@default> <dewar.873989183@merv>
 <5vaude$q20$1@goanna.cs.rmit.edu.au> <5vbiid$luu$1@goanna.cs.rmit.edu.au>
 <34197042.7CFC@gsfc.nasa.gov> <dewar.874165401@merv>
Reply-To: Stephen.Leake@gsfc.nasa.gov
Organization: NASA Goddard Space Flight Center -- Greenbelt, Maryland USA
Newsgroups: comp.lang.ada
Date: 1997-09-15T00:00:00+00:00
List-Id: <comp.lang.ada>


Robert Dewar wrote:
> 
> Stephen says
> 
> <<Unbounded strings are very nice for beginners. However, they do require
> some form of garbage collection to be used correctly. I hope that later
> in the course, this will be pointed out.
> 
> Which leads me to a question about the GNAT implementation of Unbounded
> Strings; do they have their own storage pool, and does Free compact the
> pool? One of these days I'll try to read the source.>>
> 
> When we say that something is "nice for beginners", we are presumably saying
> that students who want to write programs to do X will find it convenient to
> use feature Y. But always remember that when we teach computer science,
> writing programs as excercises is not about writing programs to do X, it is
> about learning the fundamental concepts, and techniques. The programs we write
> in class are a *means* to an end, not an end in themselves. This is a very
> improtant difference. In the world of real life application programming, the
> point is to create a working program that meets the specifications. When we
> are teaching the point is to LEARN HOW to create!

Excellent point, which I missed. It is definitely more important to
learn the fundamentals. On the other hand, if your learning control
structures, and you want to print a diagnostic message that is built
from several strings, Unbounded_Strings are nice.

 
> As to your technical question (gosh, a technical question on CLA, I had
> forgotten that this could happen :-)

Glad to oblige :)

> GNAT uses controlled types to
> implement unbounded strings. Using a special garbage collected pool is
> an interesting idea which we have thought about (and which has been discussed
> at length in previous CLA threads), but we have not yet followed up this
> idea.

As I thought. So Dale (if you're still reading :), will you be pointing
out that using Unbounded_String does have a big downside? When you get
to teaching about dynamic memory allocation and managment, you could
point out that they've been doing it all along without thinking about
it, just like a lot of professional programmers!.
-- 
- Stephe