Proposal for design of 'scope' (Was: Re: Opportunities for D)

[via Digitalmars-d]

On Thursday, 10 July 2014 at 21:01:23 UTC, Timon Gehr wrote:
> On 07/10/2014 10:10 PM, "Marc Schütz" <schuetzm at gmx.net>" wrote:
>> ...
>> Instead of lifetime intersections with `&` (I believe Timon 
>> proposed
>> that in the original thread)
>
> I didn't. I suggested that _some_ suitable syntax might need to 
> be found. :)

Apologies, then :-)

But the point still stands - I don't think we need to introduce 
"invented" lifetime names as Rust does, we can refer to existing 
identifiers/symbols instead.

>
>> The root cause of the problem here is the call to `free()`.
>
> (Proving the safety of code containing manual free requires 
> different machinery.)

I think that once manual memory management is involved, it's 
impossible to make safety guarantees in the general case. But I 
also believe that not all is lost: Much can be won when the 
_implementers_ of libraries take special care (in our case by not 
marking free() as scope), so that library _users_ cannot 
accidentally run into these problems. And because the 
trouble-makers can be clearly identified, there is even a simple 
rule that covers probably 99% of the cases: "Don't make memory 
deallocators take borrowed pointers."

The reason I'm not completely sure about it is that move 
semantics can have the same effect as manual memory management: 
It's possible to move a unique object into a lower scope, which 
is then destroyed at the end of that scope. It's just much less 
obvious...