Idea #1 on integrating RC with GC

[Adam Wilson]

On Tue, 04 Feb 2014 16:07:29 -0800, Adam Wilson <flyboynw at gmail.com> wrote:

> On Tue, 04 Feb 2014 15:51:35 -0800, Andrei Alexandrescu  
> <SeeWebsiteForEmail at erdani.org> wrote:
>
>> Consider we add a library slice type called RCSlice!T. It would have  
>> the same primitives as T[] but would use reference counting through and  
>> through. When the last reference count is gone, the buffer underlying  
>> the slice is freed. The underlying allocator will be the GC allocator.
>>
>> Now, what if someone doesn't care about the whole RC thing and aims at  
>> convenience? There would be a method .toGC that just detaches the slice  
>> and disables the reference counter (e.g. by setting it to uint.max/2 or  
>> whatever).
>>
>> Then people who want reference counting say
>>
>> auto x = fun();
>>
>> and those who don't care say:
>>
>> auto x = fun().toGC();
>>
>>
>> Destroy.
>>
>> Andrei
>
> I am assuming that you ignoring cyclic-refs for now. And dealing with  
> them would mean that you would need something like:
>
> auto @weak x = fun();
>
> Since the compiler cannot figure out that this is supposed to be weak or  
> not it would assume strong as that is the majority.
>
> Second thought. Why is their an extra step for those of us who don't  
> want the GC. I know there has to be an extra step for some people, but I  
> feel that we should make the simplest option the default and then open  
> up avenues for more advanced control for people who want it. ARC is not  
> as simple to understand as a GC for newbies, and ARC requires more  
> careful control, so why not make getting into ARC a little harder, that  
> way we prevent heartache for new people. So something more like:
>
> auto x = fun().toARC();
>
> I can't imagine any situation where you could go from ARC to GC that  
> could not also go from GC to ARC, they have to be equivalent operations  
> to do that anyways.
>
> In the design world you make the simple option easy and more the more  
> advanced options harder to get at to reduce the chance that the user  
> accidentally shoot themselves in the foot. And the guys who want to the  
> advanced options are power users anyways, they expect to have to work at  
> it a little more.
>
> Related third thought. This goes against the current paradigm and will  
> subtly break existing D code that has cyclic-refs in it.
>

Ok, disregard my previous post. I think I understand better what Andrei is  
driving at, but it's not obvious, better examples are needed. But more to  
the point this is going to make us all equally miserable. The ARC guys  
don't get the compiler support needed to make ARC fast. It completely  
ignores cyclic-refs inside the slice. It doesn't solve the primary  
ARC-camp complaint about the reliance on the GC. The GC now guys have more  
hoops to jump-through when working with Phobos. And it increases  
complexity and cognitive load all around.

-- 
Adam Wilson
GitHub/IRC: LightBender
Aurora Project Coordinator