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From: Bill Findlay <yaldnif.w@blueyonder.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: Dereferencing and style guides
Date: 11 Oct 2013 13:19:06 GMT
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Robert A Duff <bobduff@shell01.TheWorld.com> wrote:
> Bill Findlay <yaldnif.w@blueyonder.co.uk> writes:
> 
>> Can I make the contrary case?
> 
> Certainly.
> 
>> Given that we know that P is a pointer, P.f or P(i) can only reasonably be
>> interpreted as dereferencing P and selecting a component from the result; so
>> I do not see that P^.f or P^(i) improves comprehensibility to any
>> significant degree.
>> 
>> Given that we do not know that P is a pointer, P.f or P(i) is essentially
>> the same cognitive burden as R.f or A(i); from the uniform referent point of
>> view this is an advantage.  It fails to be, only if the dereference fails,
>> and we know that that should not happen in Ada 8-).  Even if it does, the
>> extra effort of perceiving the semantics correctly is trivial.
> 
> By "dereference fails", I assume you're talking about null pointers.
> I wasn't so worried about that -- I'm more worried about
> aliasing.  I'm thinking "X^.Y := ..." is a helpful reminder that
> some other pointers might also point to X^.

But even without prior knowledge that P is a pointer, there are several
ways that must be borne in mind for how P.whatever could be aliased, the
existence of another pointer with the same value as P being perhaps the
most straightforward.

{An anecdote. Many years ago I did once get major benefit from the ^
notation in Pascal.  I had to convert a program from using data in an
external file to using data in virtual memory.  I merely had to write a
"get" procedure for the latter and the rest of the code was essentially
unchanged, with data^ reinterpreted as a pointer dereference instead of a
file record access.  The point being that there was some commonality of
syntax in Pascal with ^, and there is even more in Ada without it.}

> So I'm not convinced.  But I guess your point of view is more
> popular than mine.  Consider languages like Java, for ex,
> where (almost) everything is a pointer, greatly (IMHO) exacerbating
> the aliasing problem.

Yes.  Yuck.

-- 
Bill Findlay