What's the go with the GC these days?

[Timon Gehr]

On 06.01.19 04:02, Meta wrote:
> On Saturday, 5 January 2019 at 23:51:53 UTC, Nicholas Wilson wrote:
>> On Saturday, 5 January 2019 at 22:42:11 UTC, Meta wrote:
>>> On Saturday, 5 January 2019 at 22:05:19 UTC, Manu wrote:
>>>> Is progress possible, or is the hard reality that the language is 
>>>> just designed such to be resistant to a quality GC, while the 
>>>> ecosystem sadly tends to rely on it?
>>>>
>>>> Where's the ARC stuff? What happened to opAddRef/opRelease?
>>>
>>> As per Andrei's talk at the last Dconf, ref counting requires 
>>> __mutable to play nicely with const and immutable.
>>
>> I'd rather have opHeadMutable than __mutable, does the same thing but 
>> doesn't subvert  the type system
> 
> I'm fairly dubious of adding __mutable as well, but I'm assuming the 
> previous solution of using an AfixAllocator didn't pan out.

It can't work without `__mutable` because it breaks transitivity of 
immutability. The entire point of `__mutable` is to add a transitivity 
escape hatch for (@system-level data structure and runtime 
implementations) that doesn't block high-level optimizations based on 
immutability and purity.


> I don't know 
> enough about opHeadMutable to consider whether it would address the same 
> problems.

It's orthogonal. If you have an immutable object, it can't have a 
reference to a reference count without `__mutable`. opHeadMutable can't 
change that.