Re: Implementing Rust's borrow checked pointers

[Optikos <optikos@verizon.net>]

On Tuesday, September 24, 2019 at 4:05:45 AM UTC-5, Lucretia wrote:
> Hi,
> 
> Been talking to someone on Telegraph and he was saying Ada should implement this, just wondering
> whether Ada could? I posed a slight change to access type specification to do this, what do people
> think?
> 
> type P is restricted access X;
> 
> Restricted in this case would mean that once assigned it cannot be re-assigned into or out of with out
> some sort of move operation, which could be implemented as an attribute on the access type.
> 
> A : P := L'Access;
> B : P := A'Move; --  A cannot no longer be used.
> 
> begin
>    A.all ... ; -- raises exception.

No, to be as useful as Rust's borrow checker, instead of raising exception, it needs to be a compile-time error.  The compiler needs to maintain a whole-program directed graph at compile-time, not defer a detection-based localized analysis to run-time.

> I don't know enough about all this to put a complete proposal together, but I think I've got the basics
> understood.
> 
> Luke.