From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2023-02-20 11:30:13
On 2/20/23 08:47, Gavin Lambert via Boost wrote:
> On 20/02/2023 18:25, Peter Dimov wrote:
>> Whatever your definition of equivalence, X is neither equivalent to an
>> int,
>> nor to a 'none', and 'none' doesn't even have operator==.
>
> Regarding this point specifically, the author of X has indeed declared
> that X has an equivalence to int, by implementing that operator.
>
> Being able to ask if `x == 4` inherently implies that `x` can somehow be
> equivalent to `4`. If that equivalence is not intended to be implied,
> then it shouldn't have been defined. (or perhaps a different type from
> `int` should have been used)
I think you're missing the point that operator== isn't always used to
implement equivalence. This is also true wrt. other operators and their
default function. We have a number of lambda libraries in Boost, as well
as Boost.Proto and Boost.Spirit that wouldn't have existed if we
followed your logic.