Re: Announce: The Ultimate SI Units Cracker

["Randy Brukardt" <randy@rrsoftware.com>]

Wes Groleau wrote in message <3D809F51.299A6634@despammed.com>...
>Ada 95 extended the concept of attributes being functions
>to letting them be procedures ('Write / 'Read), and 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.

>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).

>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.)

                Randy.