DIP1000: 'return scope' ambiguity and why you can't make opIndex work

[Dukc]

On Monday, 21 June 2021 at 16:56:30 UTC, Dennis wrote:
> While ptr0 can be assigned to ptr1, when going through a 
> `CustomPtr c`, dmd still sees it as assigning "scope variable 
> `c`".

I was about to say it might be that you need to write

```d
void f(scope ubyte* ptr0) {
     scope ubyte* ptr1;
     ptr1 = ptr0; // fine
     {
         auto c = CustomPtr(ptr0);
         ptr1 = c.get();with longer lifetime
     }
}
```

...instead, but that fails too, at least on 2.096 release 
canditate.

As does this one:

```d
ubyte* get(ref return scope ubyte* ptr){return ptr;}

void f(scope ubyte* ptr0) {
     scope ubyte* ptr1;
     ptr1 = ptr0; // fine
     {
         auto c = ptr0;
         ptr1 = c.get();
     }
}
```

I believe we can conclude that the field "`ref` argument / value 
return / `scope`" already reads either "`ref`" or "both", at 
least when you're returning a pointer. That being the case, your 
solution makes perfect sense.