On Mon, 25 May 2026 at 12:08, Hewill Kang via Std-Proposals <
std-proposals_at_[hidden]> wrote:

>
>> FWIW, I found it super easy to implement a proper `flat_map` that Just
>> Works for all types (even bool). I've been "shipping" it in my P1144 fork
>> of libc++ since at least January 2023, since before Hui Xie's flat
>> containers were merged to Clang trunk.
>> https://godbolt.org/z/j1az7vY87
>> These days the patch is reduced to just a few lines on top of Hui's
>> implementation:
>>
>> https://github.com/llvm/llvm-project/commit/a3cb6f367fe50ac40cefc6bced487e141f6cbe23
>>
>> I certainly think that all vendors (yes, even libc++!) should ship an
>> implementation of `flat_set` and `flat_map` that Just Works, even with
>> `bool`. I think libc++'s current behavior is deplorable.
>>
>
I think libc++'s behaviour is OK, given the current wording of the standard.


> Does that mean we need to change the wording of the paper standard? Well,
>> IMHO, vendors *should* know to Do The Right Thing regardless of whether
>> the paper standard requires it. But changing the paper standard would
>> probably help in practice, so sure, I'd encourage you to go for it.
>>
>
Do the right thing, if the right thing does not go against the standard.
Otherwise we should change the standard first.

The trick with the paper standard is that `vector<bool>` isn't a "sequence
>> container"; so either you'll have to figure out how to stretch the
>> definition of "sequence container" to include `vector<bool>`, or you'll
>> have to extend the definition of `flat_set` to include `vector<bool>` as a
>> special case. The former would be more generally useful in the future, but
>> the latter is way easier.
>>
>
I think Aryan's approach is good and simple. Also, I won't worry about
`flat_set<bool>`. Only `flat_map<Key, bool>` is likely, though, honestly
speaking, it can be replaced with `flat_set<Key>` too...