d future or plans for d3

[Timon Gehr]

On 12/19/2011 12:45 AM, Vladimir Panteleev wrote:
> On Sunday, 18 December 2011 at 23:31:03 UTC, Timon Gehr wrote:
>> On 12/19/2011 12:24 AM, Vladimir Panteleev wrote:
>>> On Sunday, 18 December 2011 at 23:18:22 UTC, Timon Gehr wrote:
>>>> You are right. I have had in mind a generational GC that uses a
>>>> copying collector for the nursery as this is what most
>>>> state-of-the-art VM GCs do.
>>> These changes are too invasive for the language at this point, I
>>> believe. We need to work with what we have.
>>
>> I disagree. Code that relies on other semantics would just have to use
>> conservative GC.
>
> Please elaborate on how you would hypothetically change D to accustom
> such changes. I am having trouble imagining such an implementation that
> would not have a considerable impact on D's performance.

If you have an union

union X{
     int  x;
     int* y;
}

The compiler would just lay out x and y sequentially instead of at the 
same memory location. Alternatively, it could add a tag to each union.

In case of passing GC memory to C functions, I would prefer to just 
disallow the C code to capture the reference, and to disable GC while 
the C function runs. (disabling and enabling GC is just a matter of 
modifying a counter somewhere, that should not visibly impact 
performance.) If C code was to capture a reference to the memory then it 
would probably take ownership anyway, which would necessitate to 
allocate the memory with malloc even with conservative GC.

I am not sure what to do about void[] though.