Re: [PATCH 1/9] Define a structure for object IDs.

[David Kastrup <dak@gnu.org>]

Johannes Sixt <j6t@kdbg.org> writes:

> Am 04.05.2014 08:07, schrieb Michael Haggerty:
>> On 05/03/2014 10:12 PM, brian m. carlson wrote:
>>> Introduce a structure for object IDs.  This allows us to obtain the benefits
>>> of compile-time checking for misuse.  The structure is expected to remain
>>> the same size and have the same alignment requirements on all known
>>> platforms, compared to the array of unsigned char.
>>
>> Please clarify whether you plan to rely on all platforms having "the
>> same size and alignment constraints" for correctness, or whether that
>> observation of the status quo is only meant to reassure us that this
>> change won't cause memory to be wasted on padding.
>
> I think that a compiler that has different size and alignment
> requirements for the proposed struct object_id and an unsigned
> char[20] would, strictly speaking, not be a "C" compiler.

Huh?  How so?  There is no warranty as far as I know that a structure
with only a single member has the same size and alignment requirements
as the single member would have.  There is also no guarantee as far as I
know that anything but element dereference is a valid means of
converting access to a struct to access to a sole element.

-- 
David Kastrup