Re: Announce: The Ultimate SI Units Cracker

[Wes Groleau <wesgroleau@despammed.com>]

Randy Brukardt wrote:
> Wes Groleau wrote in message <3D809F51.299A6634@despammed.com>...
> >Ada 95 .... allowed
> >programmers to redefine/override 'Write and 'Read.  I am curious
> >whether overriding/creating other attributes was considered.
> >Obviously, like operator overloading, it could easily be
> >used to obfuscate, but it could be very useful to be able
> >to define 'first and such for things like SI and Rational.
> 
> It was considered for Ada 9x, but was rejected as having insufficient
> value for the substantial changes that would be required for compilers.
> Most existing Ada compilers do not put attributes in the symboltable;
> they do not have visibility, and so on.

But they do for 'Write & 'Read, so why not for others?

> >It would also be nice to be able to define a type conversion.
> >
> >function Float (T : SI) return Float is ....
> 
> This was discussed recently, and it was essentially proven to be
> impossible without major incompatibilities. See ac-00026
> (http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AC-00026.TXT).

Thanks for the link.

> >What I'm getting at is the ability to define a private type
> >so that it has all the attributes and operations of a numeric
> >type and can be use as a generic parameter to a numeric package.
> 
> Someone is always dreaming about that, but no one has had anything that
> looks remotely like a viable proposal. (Numeric literals are always
> trouble, as are the type conversions.)

I can see where literals would be difficult.  But if you can
declare a local type called Float, why can't you instead call
a local function called Float?  In the case of ambiguities....
I guess I'd better follow the link before I say any more.

-- 
Wes Groleau
http://freepages.rootsweb.com/~wgroleau