czw., 6 mar 2025 o 12:17 Giuseppe D'Angelo via Std-Proposals
<std-proposals_at_[hidden]> napisał(a):
>
> Il 06/03/25 11:23, Robin Savonen Söderholm via Std-Proposals ha scritto:
>
> A simpler option would be to change the API for the minmax function (and perhaps other, similar looking functions) to something where if an RValue is detected amongst the arguments, it would return a std::pair<T, T> only (or pair<T const, T const>), while if all arguments are lvalue references it could keep it's current form (for speed or for the need of testing the address of an argument or something..)
>
> What would be the best remedy for things like this you think?
>
>
> This is the kind of things that make C++ a user-hostile language -- a lifetime trap in such a simple and basic API. I don't think we can possibly change the shape of these APIs along the lines of you describe, it'd be an API incompatible change, and lifetime isn't value category.
>
> (For instance: void f(std::pair<const int &, const int &>); f(std::minmax(a, a-b)); is OK. If you change minmax's return type you're going to break that code.)
>
>
> Your best shots are:
>
> 1) to use an up-to-date compiler: GCC 14 warns about your construct https://gcc.godbolt.org/z/Ybb7ce5Y6
>
> 2) to ban any usage of std::min/max and roll your own versions (e.g. my::min/my::max always returning values, my::min_ref/my::max_ref returning references).
>

`min` and `max` are fine, you need to explicitly ask for `&` to shoot
yourself in foot.

```
auto z = std::max(foo(), bar());
```

this will always work correctly for types that are safely copyable.

```
auto& z = std::max(foo(), bar());
```

This could be broken depending on what is returned from `foo` or `bar`.

OP simply wanted similar behavior with `minmax` but this is impossible
as we have "tuple" indirection that break `auto` in this case.

>
> --
>
>
> Regrettably, the issue you face,
> Unfortunately, can't be solved in place.
> Since the API's broken, there's no way around,
> This problem persists with no fix to be found.
>
>
> My 2 c,
>
> --
> Giuseppe D'Angelo | giuseppe.dangelo_at_[hidden] | Senior Software Engineer
> KDAB (France) S.A.S., a KDAB Group company
> Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
> KDAB - Trusted Software Excellence
>
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