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From: tmoran@bix.com
Newsgroups: comp.lang.ada
Subject: Re: Flags in Ada?
Date: 28 Oct 1994 03:59:17 GMT
Organization: Delphi Internet Services Corporation
Message-ID: <38psul$nsb@news.delphi.com>
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Date: 1994-10-28T03:59:17+00:00
List-Id: <comp.lang.ada>

Some downsides of using 9X modular types:

 Console.Control := Start_Read_Bit;
may look correct, but perhaps what you really wanted was
 Console.Control := Console.Control or Start_Read_Bit;

Using records, those two are done with less ambiguity with
 Console.Control := Start_Read_OP_Code;
 Console.Control.Start_Read := True;

>...  a measure of safety.  The compiler will complain if you
>use a Status_Byte mask on the Control register, or vice-versa.

But    Console.Control := Console.Control*3;   is legal, though
perhaps not what you meant to code.  And there is a temptation
to do arithmetic (shift, for instance) to accomplish things.
In some circumstances that's fine, and even a good reason to use
modular types rather than records, but it clearly locks you
into a certain bit representation.  There are plenty of programmers
in the world who will do 'clever' arithmetic to juggle bits. :(