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From: Frank D. Engel, Jr.
Subject: [GPC]: daily digest (#613)
Date: 1 Feb 2005, 14:50:00

Hash: SHA1

On Feb 1, 2005, at 1:59 PM, Frank Heckenbach wrote:

> issues. Since Ada's main goal is to be strongly typed and safe at
> runtime, I can't really imagine they added things such as unchecked
> type-casts, "absolute" variables, assembler statements and machine
> code inlines, low-level memory access (FillChar, Move), misusing
> constants as variables, confusion between pointers and arrays and
> sometimes single elements and arrays etc., to name just some of the
> most problematic ones.


Correct, those are not features of Ada.  Ada *does* have features like 
AND THEN and OR ELSE (like GPC's AND_THEN, OR_ELSE), and a number of 
really cool features that are not even part of GPC to my knowledge.  
Then again, GPC has some things (like SETs) which Ada does not...

Ada has the notion of a "range", which is a sequence of values with a 
starting point and an ending point.  In other words, a range could be 
1..5, 'a'..'z', etc., but it cannot contain disjoint values as can one 
of Pascal's SETs -- ['A', '5'..'7'] cannot be reproduced easily in Ada.

However, you can do some interesting things with the ranges:

for i in 1..5 loop   -- standard Ada for loop header

for i in Integer'Range  -- another way to look at it, hmm...

Ada *does* have type casts, but they are neither 'unchecked' nor 
arbitrary.  Additionally, you can't even directly perform mathematical 
operations between integers and reals without casting them.  Ada is 
very picky, but it certainly does make it much more difficult to 
accidentally leave many kinds of "stupid" bugs in your code.  
Off-by-one is still possible, obviously (although Ada can even catch 
some instances of this, where types are well-defined and the off-by-one 
results in a range check exception), and some other things...

Ada also supports exceptions, and a somewhat strict variation on 
inheritance using extensible records:

type oldRec is
     record
         oldField : Integer;
     end record;

type newRec is new oldRec with
     record
         newField : Integer;
     end record;

(newRec will have two fields: oldField and newField).


Disclaimer: I did not run the above code through an Ada compiler, so it 
is quite possible there were some errors in that code... but I'm sure 
it's pretty close.

- -----------------------------------------------------------
Frank D. Engel, Jr.  <fde101@fjrhome.net>

$ ln -s /usr/share/kjvbible /usr/manual
$ true | cat /usr/manual | grep "John 3:16"
John 3:16 For God so loved the world, that he gave his only begotten 
Son, that whosoever believeth in him should not perish, but have 
everlasting life.
$

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