Re: [boost] [serialization] patch for portable_binary_oarchive.hpp

From: David Abrahams (dave_at_[hidden])
Date: 2007-11-02 22:35:05

on Fri Nov 02 2007, "Peter Dimov" <pdimov-AT-pdimov.com> wrote:

> Boris Gubenko:
>
>>> I think the correct change to silence the type conversion error is
>>>
>>>   char * first = static_cast<char *>(static_cast<void 
>>> *>(const_cast<long*>(&
>>> l)));
>>
>> I'm not sure my change is incorrect. In terms of style, I think that your
>> change is better.
>
> Dave's insistence that we have to obfuscate our reinterpret_casts is
> well known and a very strict reading of the standard is on his side
> _in this specific case_, but I personally don't find his style
> better at all.

Me neither.  But that's the way it is.

BTW, when I asked this question of the standard committee's core
working group, the response was a kind of stunned surprise that anyone
would even ask, and aside from one person, they all thought it was
obviously true that static_cast-ing through void was the only correct
thing to do.

> (A reinterpret_cast<char*>( p ) is indirectly required to work when
> p is a pointer to a class type,

Where does the standard say that, and what
do you mean by "work?"

As far as I know the only things that reinterpret_cast is required to
work for are round-trip pointer conversions and -- if a suitable
integer type exists -- some kind of conversion of pointers into
integer types.

> but it's possible in theory for a sufficiently mischievous compiler
> to break it for long*. I know of no such compiler, present or
> future, of course.)

And most probably won't, because reinterpret_cast is so widely used
with the assumption it does what everyone wants.  However, we might
want Boost code to pass cleanly through code verification tools, for
example.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com