On Sunday, 12 April 2015 at 04:18:54 UTC, Andrei Alexandrescu wrote:
> On 4/11/15 5:35 AM, matovitch wrote:
>> I am not convinced by the dip77, what about raii managed classes with
>> costly opAssign operator (like in w0rn example) ? The goal of passing an
>> object by reference is to avoid the copy and here you guess the
>> parameter is ref-counted and made a (pseudo-)copy ? Then any allocating
>> opAssign should be marked @system ?
>
> Expensive opAssign or expensive postblit? -- Andrei

Well both in the example given by w0rp. I guess D as no "rule of five" but still a "rule of three" (which is in fact rule of four with the copy-and-swap idiom) about coding posblit, opAssign and destructor together ?

On Sunday, 12 April 2015 at 07:17:07 UTC, Walter Bright wrote:
>
> A quick read of this suggests it is doing the Rust model of only one mutable reference at a time. Is this really viable with D?

I would love to see a storage class to add the rust ownership model to D. I surely don't know if it's feasible.

On Saturday, 11 April 2015 at 20:40:20 UTC, deadalnix wrote:
> On Saturday, 11 April 2015 at 09:28:46 UTC, Marc Schütz wrote:
>> It's not acceptable that it happens behind the user's back. Costly operations must be explicit.
>
> Nothing is costly here.

Of course it is:
http://forum.dlang.org/post/iehijjgdlfouplcngrjy@forum.dlang.org

On Sunday, 12 April 2015 at 07:17:07 UTC, Walter Bright wrote:
> On 4/11/2015 4:33 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm@gmx.net>" wrote:
>> http://wiki.dlang.org/User:Schuetzm/scope3#.40safety_violations_with_borrowing
>
> A quick read of this suggests it is doing the Rust model of only one mutable reference at a time. Is this really viable with D?

I think it is. You have to keep in mind that this is opt-in; it only applies to `scope` variables. I would agree that as a default, it wouldn't fit D at all. I think that, for all its usefulness, it'd be a tad too limiting for my taste if I were forced to use it everywhere. In Rust, it needs to be ubiquitous, because their goal is to get by without a GC. We on the other hand just want a way to make the GC easier to avoid. We also want to be able to use these different programming styles side by side, therefore an opt-in solution is good.

Besides, I too want to recommend the article Matovitch linked to, and Yehuda Katz' article mentioned therein, because they make a good point demonstrating that it gives more correctness guarantees than just memory safety:

http://forum.dlang.org/post/ttjzihuffrdlgqonqiwi@forum.dlang.org

It's a great building block for lots of nice things. In fact, it's quite likely the only way to get these guarantees once you look beyond reference counting.

Marc Schütz:

> You have to keep in mind that this is opt-in; it only applies to `scope` variables. I would agree that as a default, it wouldn't fit D at all. I think that, for all its usefulness, it'd be a tad too limiting for my taste if I were forced to use it everywhere.

I think D Zen asks for safety on default and opt-out on request.

See also "@safe by default":
https://issues.dlang.org/show_bug.cgi?id=13838

Bye,
bearophile

On Sunday, 12 April 2015 at 12:06:50 UTC, bearophile wrote:
> I think D Zen asks for safety on default and opt-out on request.

Marc talked about unique ownership vs. shared ownership, not about safe vs. unsafe.

On Sunday, 12 April 2015 at 07:17:07 UTC, Walter Bright wrote:
> On 4/11/2015 4:33 AM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm@gmx.net>" wrote:
>> On Saturday, 11 April 2015 at 09:41:07 UTC, Walter Bright wrote:
> A quick read of this suggests it is doing the Rust model of only one mutable reference at a time. Is this really viable with D?

It's a very good ownership model IMO, because it has no runtime overhead and often sharing/escaping isn't needed. Would at least be interesting to explore this in more detail for scoped variables.

As a side note, I find that unique ownership is strangely missing from our discussions, yet it's a perfect ownership model for resources such as a File.
https://github.com/D-Programming-Language/phobos/pull/3171

On Sunday, 12 April 2015 at 13:12:05 UTC, Martin Nowak wrote:
> As a side note, I find that unique ownership is strangely missing from our discussions, yet it's a perfect ownership model for resources such as a File.
> https://github.com/D-Programming-Language/phobos/pull/3171

I'm aware of it, but didn't want to open another can of worms. I have a vague idea what to do about it, based on deadalnix' "isolated" idea and the already existing uniqueness concept. I need to make up my mind about moving though, whether the benefits of making the compiler know about it are worth the added complexity.

Am Sat, 11 Apr 2015 20:42:52 +0000
schrieb "deadalnix" <deadalnix@gmail.com>:

> On Saturday, 11 April 2015 at 18:20:51 UTC, Marco Leise wrote:
> > Am Fri, 10 Apr 2015 14:04:39 +0000
> > schrieb "Ola Fosheim Grøstad"
> > <ola.fosheim.grostad+dlang@gmail.com>:
> >
> >> On Friday, 10 April 2015 at 10:28:03 UTC, Walter Bright wrote:
> >> > That's what ref counting is about.
> >> 
> >> That would require pervasive ref-counting.
> >
> > You make is sound like there was an alternative to ref counting for resources. Is there?
> 
> Ownership, GC.

That doesn't convince me yet. GC is just incorrect to use here. D's GC like any other that is non-deterministic will hold on to many external resources for longer than is feasible.

(Unique) ownership on the other hand isn't really what we are
looking at here, right? I mean, the DIP talks about what
happens when you are dealing with multiple references to
the same item.

That leaves us with RC, which I think is a good choice.

-- 
Marco