I came up with this (quite ugly) implementation:

struct Vec3 {
    union {
        float my_vec[1];
        float x;
    };

    float y;
    float z;
};
This will probably be flagged by sanitizers and some compilers as unsafe, but I believe it's standard-compliant and does what's asked for.





On Fri, Mar 8, 2024 at 2:53 PM Jens Maurer via Std-Proposals <std-proposals@lists.isocpp.org> wrote:


On 08/03/2024 00.23, veronica alphonso via Std-Proposals wrote:
> The issue i see about making anonymous structs/classes standard, is that now something as confusing as this could be allowed:
>
> // on the global namespace...
> struct
> {
> int x;
> };
>
> void foo()
> {
>     .x = 42;
>     // what? so x is some kind of weird SDM/global now?

What is "SDM"?

>     // what is its lifetime?
> }

We already have anonymous unions, suitably restricted to being
members of classes only.

Given those restrictions, how much of the problem space would
anonymous structs address?

Jens


> El jue, 7 mar 2024 a las 23:17, Sebastian Wittmeier via Std-Proposals (<std-proposals@lists.isocpp.org <mailto:std-proposals@lists.isocpp.org>>) escribió:
>
>     __
>
>     Dear Veronica,
>
>     what about your mentioned alternative of anonymous unions and structs?
>
>     They could be made standard-compliant.
>
>     And would need less language changes.
>
>      
>
>     Would they have problems with UB due to which element is the active one? When used in your use case?
>
>      
>
>     Best regards,
>
>     Sebastian
>      
>
>         -----Ursprüngliche Nachricht-----
>         *Von:*        veronica alphonso via Std-Proposals <std-proposals@lists.isocpp.org <mailto:std-proposals@lists.isocpp.org>>
>         *Gesendet:*   Do 07.03.2024 23:55
>         *Betreff:*    [std-proposals] Subscript aliasing
>         *An:* std-proposals@lists.isocpp.org <mailto:std-proposals@lists.isocpp.org>;
>         *CC:* veronica alphonso <verodeving@gmail.com <mailto:verodeving@gmail.com>>;
>         In C++ there isn't a standard-compliant way of creating named aliases of c-like array elements. In certain contexts, it is preferred to access these these array elements with a named identifier that is bounded to that particular array entry, e.g:
>
>         union
>         {
>             float my_vec[3];
>             struct
>             {
>                 float x, y, z;
>             };
>         };
>
>         However, anonymous structs/classes are only
>
>         --
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>
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