Re: [review][fixed_string] End of review periodapproaching and a plea

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2019-12-04 23:19:50

On 2019-12-05 01:24, Peter Dimov via Boost wrote:
> Krystian Stasiowski wrote:
>> On Wed, Dec 4, 2019 at 1:24 PM Peter Dimov via Boost 
>> <boost_at_[hidden]> wrote:
>>
>> > Yes, probably. As I said, it's not clear that we should bother with 
>> it > (I wouldn't), but it at least gives consistent space savings for 
>> all > short strings.
>> >
>> > That said, one could use it for N < 32, when the size will be in the 
>> > same cache line.
>>
>> Â  What should I do? I can implement this, but since `size()` would be 
>> have to be called as opposed to simply accessing the member (this 
>> already happens, since a proxy function is used due to the 
>> specialization for zero size, but it only returns the member each time 
>> so it is easily inlined), as Andrey mentioned this may not be cache 
>> friendly.
> 
> Well as I said, if it were up to me, I wouldn't use this optimization.
> 
>  Â Â  smallest_width_t size_;
>  Â Â  char data_[ N+1 ];
> 
> is good enough for me, in all cases, including N == 0. This makes 
> fixed_string<0> two bytes instead of one, but I'm pretty sure I (and 
> 99.4% of the Earth population) can live with that.

I think, fixed_string<0> should be specialized to an empty class. Not 
that I have a specific use case for fixed_string<0>, but making the 
class empty in general is useful for EBO and [[non_unique_address]] and 
e.g. tuples that employ these techniques. If we can attach the attribute 
to a captured value in a lambda, that'd be useful as well.