Re: Teaching new tricks to an old dog (C++ -->Ada)

["Jerry Coffin" <jcoffin@taeus.com>]

Dr. Adrian Wrigley wrote:

[ ... ]

> Isn't there some confusion here?
>
> Surely the "aliasing" issue (ignored by C++ completely(?)) is largely
> independent if the "reinterpret_cast"/"Unchecked_Conversion" issue?

Yes -- he started by mentioning aliasing, but mostly seemed to be
talking about type punning, so that was what I replied to. The
discussion centered around safety, which is essentially orthogonal to
aliasing.

> The C++ programmer uses aliasing routinely and without thinking.

Aliasing is used frequently in C++, that much is true. IMO, the claim
that it's done "without thinking" is nothing more or less than flame
bait. I think you're capable of better.

> Ada makes the aliasing possibility explicit when necessary, but
> prohibits it otherwise.

Aliasing is almost certainly more common in C++, but ultimately it only
ever happens explicitly in either language. In fact, I think "explicit"
is virtually meaningless in discussing a programming language -- the
processor is not an intelligent being that makes decisions on its own
unless explicitly directed. As such, nothing in code is really
implicit. What most people call "implicit" is simply the rules of the
language doing their job. Even those who push explicitness as a virtue
rarely do things like parenthesizing a+(b*c). Even those who argue most
strongly for explicitness generally agree that this would be silly, at
least in "obvious" cases like the one above.

The "implicit" behavior I've seen Ada programmers complain about in C++
is equally codified in the rules of the language, and the fact that Ada
programmers think it's somehow implicit mostly just reflects the fact
that they don't know those rules. That's fine, but condemning the
language simply because they don't know it is much less so.

> If we're talking about the "reinterpret_cast" issue, it is
> essentially identical in Ada.

...and this is what actually affects safety. Aliasing mostly just makes
it more difficult to generate efficient code. Despite this, most claims
that C and/or C++ produce particularly poor code show little more than
defects in the testing.

--
    Later,
    Jerry.

The universe is a figment of its own imagination.