span cannot, in all cases, validate the index of operator[] at compile
time. Compare to [], for most containers, that's one reason why at()
exists, to generated an exception at run time. The CppCoreGuidelines (
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#slcon3-avoid-bounds-errors)
recommends using it to avoid bound errors. There std::string_view::at()
so why not for span ?


On Tue, Apr 14, 2020 at 10:02 PM Vishal Oza via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> I believe the issue is the at() function has exception handling for out of
> bound errors. std::span checks bounds at compile time so the error handling
> is redundant. There is an inefficiency to have out of bounds exception
> handling even if you never use it. Zero work is always faster then work
> that is never used.
>
> On Tue, Apr 14, 2020 at 8:52 PM Mario Charest via Std-Proposals <
> std-proposals_at_[hidden]> wrote:
>
>>
>> Hello,
>>
>> What is the rational for std::span not having an at() fonction, like most
>> other contiguous container.
>>
>> Regards,
>>
>> - Mario
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