Re: Refactoring and Ada

["Pat Rogers" <progers@classwide.com>]

"martin.m.dowie" <martin.m.dowie@ntlworld.com> wrote in message
news:UHS88.8818$as2.1569475@news6-win.server.ntlworld.com...
> > > How about removing the 'confirming enumeration rep specs' that
> > > are no longer necessary in Ada95?
> [snip]
> >
> > They weren't necessary in Ada 83 either were they?
>
> My understanding was that there was no requirement for a compiler
> to select a contiguous range of values from 0. So while I never actually
> came across a compiler that didn't do this, for the sake of portability
> they were always added where we cared about the underlying rep.
>
> Thankfully, we don't have to add this 'noise' anymore :-) but there
> must be thousands of lines of code like this around cluttering up code.
> From memory Robert Dewar once mentioned that these statements
> were actually dangerous (my word not his!) in Ada95. Presumably as a
> compiler may mistake them for some sort of 'special case' and produce
> some less than optimal code.

The issue is indeed performance.   (The special case to be recognized by the
compiler is that the clause is in fact a confirming rep clause.)  The semantics
have to be maintained -- eg, array indexing and for-loop iterations -- but the
compiler will produce comparably inefficient code unless the special case is
recognized.  (Most do.)  Think about how array element address calculation would
work using arbitrarily ascending values for the indexes, and the problem becomes
evident.

---
Patrick Rogers                       Consulting and Training in:
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