Re: Enumeration representation clause surprise.

[Keith Thompson <kst-u@mib.org>]

Mike Silva <snarflemike@yahoo.com> writes:
> On Jun 12, 2:41�pm, Markus Sch�pflin <nos...@nospam.org> wrote:
>> Mike Silva schrieb:
[...]
>> > Are you saying now that there's no problem after all?
>>
>> Not at all. The memory layout of the variables is not what I expect it
>> to be, because the compiler silently biased those values. The compiler
>> is perfectly aware of this, as it makes up for the biasing when
>> explicitly querying the value, but this doesn't help at all because I'm
>> interested in the exact bitwise representation.
>>
>> Admittedly, there is an inconsistency in what I'm asking the compiler to
>> do, but that's the whole point: I do not want this inconsistency to be
>> silently 'fixed' by the compiler, I want to get noted about my error to
>> get a chance and fix it myself.
>
> I wonder then if this is an error at all.  IANALL, but if the program
> makes available your specified values when queried with the proper
> mechanism (in this case, unchecked conversion), then I don't see what
> difference it makes how it stores the representations in raw memory.
>
> I'd welcome other comments on the validity or non-validity of this
> view.

If it doesn't make any difference how the representations are stored
in raw memory, then you wouldn't use a representation clause; you'd
let the compiler make any decisions about representation, subject to
the constraint that the code has to produce the right answers.

But if you *do* provide a representation clause, then the
representation clearly *does* matter.  And if the compiler can't
satisfy the requested representation (e.g., because two representation
clauses contradict each other), then the compiler should reject the
compilation unit.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"