On 2023-01-30 at 12:20, Giuseppe D'Angelo via Std-Proposals wrote:
> Hello,
>
> Il 30/01/23 07:04, Jason McKesson via Std-Proposals ha scritto:
>> On Sun, Jan 29, 2023 at 8:36 PM Giuseppe D'Angelo via Std-Proposals
>> <std-proposals_at_[hidden]> wrote:
>>>
>>> Hello,
>>>
>>> Il 29/01/23 22:11, Jason McKesson via Std-Proposals ha scritto:
>>>> On Sun, Jan 29, 2023 at 3:41 PM Giuseppe D'Angelo via Std-Proposals
>>>> <std-proposals_at_[hidden]> wrote:
>>>>>
>>>>> Hello,
>>>>>
>>>>> As per subject, I've been working on a proposal for a standardized way
>>>>> to detect if a trivially default constructible type can be value
>>>>> initialized by using `memset(0)` on some suitable storage.
>>>>>
>>>>> A draft is available here:
>>>>>
>>>>> https://isocpp.org/files/papers/D2782R0.html
>
> I've updated the draft incorporating many of the raised comments.
>
>
>>>> However, I would suggest that it should be equally true/false for all
>>>> pointers of the same category: object pointers, function pointers, and
>>>> member pointers. Either all object pointers are
>>>> trivially-zero-initializable or none of them are. Etc.
>>>
>>> Is there any reason for this? On Itanium, pointers to objects and to
>>> functions can be zero-filled. Pointers to data members cannot. Why not
>>> having the trait giving the factually correct answer? Surely one would
>>> want a vector of `string_view`s to be zero-filled.
>>
>> I may not have explained what I meant very well.
>>
>> There are 3 categories of pointers: object pointers, function
>> pointers, and member pointers. All pointers of a *particular* category
>> have to give the same answer. So all object pointers are either
>> trivially zero initializable or not. But all function pointers could
>> have a *different* answer. Etc. So on Itanium, they could have
>> function and object pointers be trivially zero initializable, but not
>> member pointers.
>>
>> What it can't do is have `int*` be trivially zero initializable but
>> `float*` not be.
>
> Ok, I got it now. But again, why imposing anything? We're entirely in
> implementation-defined territory. "Who cares" if on some fancy
> architecture `int *x=0;` is zero-filled and `float *y=0;` is not? The
> compiler will tell you the truth for each different type.
>

I care if the code happens to compile on my machine, but nowhere else.

Where is the portability, and how do you test the code?