Re: How to get a »Conventional Ada Library« (Was: Ideas for Ada 200X)

["Robert I. Eachus" <rieachus@comcast.net>]

Marin David Condic wrote:

> I like having the standard and the ARM being as thorough as it is. I'd 
> just like to see a mechanism for getting things like library components 
> "standardized" across compilers without needing to go through all the 
> rigamarole that has to happen in order to update the ARM. Had such a 
> mechanism been in place, getting the numerics packages added at a 
> post-Ada83 date would have been a piece of cake. It would also enable us 
> to get extensions to the language capabilities done in some cycle time 
> smaller than 10 years.

We (meaning the ARG and compiler vendors) have been getting better at 
that.  But even with unlimited money, standards move very slowly.

The other thing that you have to remember is that the programming 
culture around Ada had not developed when the original ANSI standard was 
produced.  I was surprised, and so were a lot of other people, at how 
the Ada culture developed in a way that was loathe to use almost 
anything that wasn't in the standard.

Even more surprising was the antipathy towards using representation 
attributes and other Chapter 13 features.  By the time the 9X effort was 
underway, no one was really surprised by the number of change requests 
that basically translated to, "We want to do unchecked conversions, but 
our coding standards don't allow us to use Unchecked_Conversion."

A sort of funny story about this happened when Dave Emery, Ben Brosgol 
and I published the ADAR components. I got a call from Rational.  My 
code wouldn't compile because it had an Unchecked_Conversion to an 
access type, and the Rational compiler didn't allow that.  I explained 
nicely that this particular use would be eliminated in Ada 9X by child 
packages, and I had done it to keep the visible package interface clean. 
  Then I told him how to modify the code to work in the Rational 
environment.

Afterwards, I asked why Rational thought it was so important to protect 
users from this particular use of Unchecked_Conversion.  He explained 
how Rational mananged storage and how it would be broken by converting 
an address to a pointer.*  I said, "But in this case I am using 
Unchecked_Conversion to convert to an object of a private type to 
itself!"  He looked at the code a bit more and said, "Maybe we should 
allow converting access types to access types..."

I don't know if Rational did modify their compiler.  But the point is 
that Rational, and their customers, thought that limiting the use of 
Unchecked_Conversion was a good thing.  Even in this case, where as I 
said, in Ada 95, one package would be a child of the other, so no 
conversion, checked or otherwise, would be required.

*Yes, they did garbage collection on the Rational hardware, but I don't 
think Rational does full garbage collection anymore.

-- 
                                                     Robert I. Eachus

"Quality is the Buddha. Quality is scientific reality. Quality is the 
goal of Art. It remains to work these concepts into a practical, 
down-to-earth context, and for this there is nothing more practical or 
down-to-earth than what I have been talking about all along...the repair 
of an old motorcycle."  -- from Zen and the Art of Motorcycle 
Maintenance by Robert Pirsig