Idea #1 on integrating RC with GC

[Jameson Ernst]

I'm just a casual end-user of D, but have been following this and 
related discussions with great interest. Just yesterday I was 
trying to "sell" D to a friend, and he basically told me that 
he'd be interested once the memory management situation gets 
resolved. I've been thinking about this a lot lately, even though 
I'm probably way out of my depth given the experts that frequent 
this forum. Still, I had an idea about this and thought I'd throw 
it out there.

On Wednesday, 5 February 2014 at 04:18:49 UTC, Andrei 
Alexandrescu wrote:
> On 2/4/14, 5:12 PM, deadalnix wrote:
>> That being understood, I'd rather connect things the other way 
>> around.
>>
>> auto x = foo();
>> auto x = foo().toRC();
>
> I don't know how to implement that.
>
>
> Andrei

 From the discussion currently going on about postblits, it seems 
like there's a new emerging concept of a "unique expression," the 
value of which is guaranteed not to be referenced elsewhere. 
Could this concept perhaps be leveraged to go backwards from GC 
to RC? If you perform a GC allocation in the context of a unique 
expression, would it then be safe to force it back into an RC 
context, knowing that there are no outstanding references to it? 
What's more, it would allow library writes to mostly perform 
allocations a single way, giving the choice to the caller how 
they'd like to manage the lifetime of the newly returned unique 
object.

I could be completely misunderstanding the unique-expression 
concept though.