Re: Thinking of using Ada for a job at home. Couple of questions first.

[John McCabe <john@nospam.assen.demon.co.uk.nospam>]

Hi Jeff

"Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org> wrote:

>John McCabe wrote:
>> 
>> The second question is related to the implementation of the System
>> Exclusive messages. Basically this is part of the reason I thought Ada
>> would be good for this task. The SysEx messages basically consist of a
>> smallish header and a variety of different structures that are
>> differentiated by the "Function" type in the header. Now I seem to
>> remember from when I did use Ada that it's possible to define the
>> record representation of a variant record such that the discriminant
>> is held within the body of the record. This would mean (I think) that
>> I could read a block of data from the synthesizer straight in to a
>> buffer that overlaid the variant record and essentially automatically
>> created a record that could be read as the particular variant related
>> to the incoming data. However I also seem to remember that's not quite
>> a 'recommended' way of doing that sort of thing. The other thing that
>> guided me in Ada's direction is that the structure of the SysEx
>> messages requires a lot of bit-fields and I'm well aware that Ada's
>> representation clauses are fantastic for that sort of thing.
>> 
>> So, in principle, would that be the way to do this, or would you be
>> able to suggest a better mechanism?
>
>That is the way I would approach this, though I might keep the buffer and record 
>separate and use Unchecked_Conversion.

Thanks for taking the time to answer that. The Unchecked_Conversion
option was the other thing I was thinking of.

>I can't tell you whether the tagged approach would work, because programming by 
>extension is a bad idea, and I avoid it whenever possible.

It's a good laugh though, and can be a useful think to know about if
your work doesn't involve anything that needs to be particularly fast,
reliable or safe :-}