On Mon, Dec 19, 2022 at 8:32 AM Vladimir Grigoriev via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> There is another unclear phrase in the C++ 20 Standard relative to
> comparison operators.
>
> «3 The return value V of a defaulted == operator function with parameters
> x and y is determined by comparing corresponding elements xi and yi in the
> expanded lists of subobjects for x and y (in increasing index order) until
> the first index i where xi == yi yields a result value which, when
> contextually converted to bool, yields false. If no such index exists, V is
> true. Otherwise, V is false.»
>

It would be helpful if you would point out *where* these phrases exist in
the C++20 Standard, as it would make it easier for people to answer your
questions. In this case, this is [class.eq]/3 (
https://eel.is/c++draft/class.eq#3)


>
> What does the last statement « Otherwise, V is false.»» mean?
>

> Does it mean a case when two expanded lists are unequal or something else?
>

No, the expanded lists have to be equal - we have the same type on both
sides. There are two separate things going on in this paragraph:


   1. What work is done? We compare xi == yi until the first i for which xi
   == yi, contextually convertible to bool, yields false.
   2. What value is returned? If no such i exists, V (the return value) is
   true. Otherwise, V is false.

Introducing V doesn't seem like it adds anything, if the wording said "If
no such index exists, the return value is true. Otherwise, the return value
is false." it'd be more direct.


> In any case a code example of such «otherwise» along with the example of a
> trivial comparison that follows would be useful to make the statement more
> clear.
>
> With best regards
> (Vlad from Moscow)
> You can meet me at http://cpp.forum24.ru/ or www.stackoverflow.com or
> http://ru.stackoverflow.com
>
>
>
> Понедельник, 19 декабря 2022, 14:33 +03:00 от Edward Catmur via
> Std-Discussion <std-discussion_at_[hidden]>:
>
>
> On Mon, 19 Dec 2022, 11:31 Vladimir Grigoriev via Std-Discussion, <
> std-discussion_at_[hidden]
> <//e.mail.ru/compose/?mailto=mailto%3astd%2ddiscussion_at_[hidden]>>
> wrote:
>
> Can anybody translate this phrase from the C++ 20 Standard
>
> «Name lookups in the defaulted definition of a comparison operator
> function are performed from a context equivalent to its function-body.»
>
> to the human language?
>
> How can a context be equivalent to a function body? They are two
> different notions.
>
>
> A context equivalent to the context of the function body.
>
>
>
>
> With best regards
> (Vlad from Moscow)
> You can meet me at http://cpp.forum24.ru/ or www.stackoverflow.com or
> http://ru.stackoverflow.com
> --
> Std-Discussion mailing list
> Std-Discussion_at_[hidden]
> <//e.mail.ru/compose/?mailto=mailto%3aStd%2dDiscussion_at_[hidden]>
> https://lists.isocpp.org/mailman/listinfo.cgi/std-discussion
>
> --
> Std-Discussion mailing list
> Std-Discussion_at_[hidden]
> <http:///compose?To=Std%2dDiscussion_at_[hidden]>
> https://lists.isocpp.org/mailman/listinfo.cgi/std-discussion
>
>
> --
> Std-Discussion mailing list
> Std-Discussion_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-discussion
>