Feature: `static cast`

[Paul Backus]

On Monday, 3 July 2023 at 17:51:19 UTC, Nick Treleaven wrote:
> I tried but it doesn't seem to work:
>
> ```d
> class C
> {
>     int* opCast(T)()
>     if (is(T == void*)) => new int(42);
> }
>
> void main()
> {
>     C c;
>     auto p = cast(void*)c;
>     pragma(msg, typeof(p)); // void*
> }
> ```

It calls `opCast`, and then implicitly converts the result from 
`int*` to `void*`. You can see it if you add a side effect to 
`opCast`:

```d
class C
{
     int* opCast(T)()
     if (is(T == void*))
     {
         import std.stdio;
         writeln("Called opCast"); // will be printed
         return new int(42);
     }
}
```

And if you change `opCast` to return an incompatible type like 
`int`, you will get a message about a failed implicit conversion:

```d
class C
{
     int opCast(T)() if (is(T == void*)) => 42;
}
// Error: cannot implicitly convert expression
// `c.opCast()` of type `int` to `void*`
```