Idea #1 on integrating RC with GC

[Adam Wilson]

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.

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