Preview features status?

[evilrat]

On Wednesday, 19 May 2021 at 07:36:53 UTC, evilrat wrote:
>
> -preview=rvaluerefparam
> This one helps with C++ interop where it's the norm but is PITA 
> in D.

Well, ok D still got me sometimes even with that preview feature, 
this s**t isn't even fun...

```d
// PxVec3 operator-
public PxVec3 opBinary(string op : "-")(ref const(PxVec3) v) 
const {
     return PxVec3(x - v.x, y - v.y, z - v.z);
}
	
public float distance(ref const(PxVec3) p) const {
     return p.dot(n) + d; // dot is also const
}

// original code, n is plain PxVec3, not const
public PxVec3 project(ref const(PxVec3) p) const {
     return p - n * distance(p); // error
}
```
> Error: incompatible types for `(p) - 
> (this.n.opBinary(this.distance(p)))`: `const(PxVec3)` and 
> `PxVec3`

```d
// lets try this
public PxVec3 project(ref const(PxVec3) p) const {
     PxVec3 t = p;
     return t - n * distance(t); // error
}
```
> Error: incompatible types for `(t) - 
> (this.n.opBinary(this.distance(t)))`: both operands are of type 
> `PxVec3`

```d
// ok, no error
public PxVec3 project(ref const(PxVec3) p) const {
     auto t = n * distance(p);
     pragma(msg, typeof(t)); // PxVec3
     return p - t; //
}

U MAD BRO?
```