`alias x = v.x;` not working in struct bodies?

[Basile B.]

On Saturday, 20 January 2024 at 09:00:22 UTC, Danilo wrote:
> I thought this should easily work, but I was wrong:
>
> [...]

Those actually would not be aliases but more _"parameter-less 
expression macros"_.

In order to make those aliases working, it would be necessary to 
monomorphize and recontextualize the source expression for each 
use:

```d
struct Vec3 {
     Vec2 v;
     alias x = v.x; // cannot contextualize, no "this"
}

Vec3 v1, v2;

v1.x = 0; // -> create v1.v.x, contextualize
v2.x = 0; // cannot reuse, "this" has changed
           // you have to copy and recontextualize
```

So you think that it's nice but it's actually more like a mixin.

An old PR would have allowed that but quickly a reviewer 
[noticed](https://github.com/dlang/dmd/pull/11273#issuecomment-660675187) that these are not classic aliases, but something more complex, bringing possible issues.

On top of that, as there's no "scope", contextualization can lead 
to ambiguous situations, reproducing the problem of what is 
called "unhygienic macros"... although for dot chains, that 
should not happen too much 🤞😐🤞.