On 1 November 2023 20:59:49 UTC, Arthur O'Dwyer via Std-Proposals <std-proposals_at_[hidden]> wrote:
>On Wed, Nov 1, 2023 at 3:09 PM Giuseppe D'Angelo via Std-Proposals <
>std-proposals_at_[hidden]> wrote:
>
>> On 01/11/2023 02:45, Hewill Kang via Std-Proposals wrote:
>> > Ranges adaptors *do* provide (explicit) operator bool since they all
>> > derived from ‘view_interface’.
>>
>> With this precedent, for better or worse, I'd say that the decision has
>> already been taken, and operator bool() should be added to all
>> containers. It makes very little sense that
>> if (vector)
>> doesn't compile, but
>> if (views::all(vector))
>> does.
>>
>
>For the record, I'm personally strongly against this proposal. It's bad
>enough that `optional<T>` is truthy; we really don't want `string` and
>`span` and so on also gaining truthiness. In a perfect world, we'd simply
>*remove* the implicit conversions from all the things that *currently* have
>them. (But of course we can't, because Hyrum's Law.)
>In particular, as others have pointed out, it would be insane for
> if ("")
>to be truthy but
> if (""sv)
>to be falsey.
>
>If you want to check something for emptiness, just check .empty().
>And if you've got a type that "can be empty" but fails to provide .empty()
>as a member function, file a DR! LWG is fixing iota_view
><https://cplusplus.github.io/LWG/issue4001> as we speak, and my own P3016 fixes
>std::initializer_list
><https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p3016r0.html>.
>But nota bene, "empty" is not the same thing as "disengaged" is not the
>same thing as "null" is not the same thing as "zero-valued." These are
>fundamentally distinct concepts, and it's important that they have distinct
>names in the C++ standard library.
>
>–Arthur

It is also problematic in case of a set of function overload that takes book and not your exact container; might end up calling the wrong function instead of a compile error