Fast GC allocation of many small objects

[Per Nordlöw]

On Monday, 2 April 2018 at 18:22:43 UTC, Steven Schveighoffer 
wrote:
> You may be interested in this proposal, which was inspired by 
> trying to implement a reserve feature for AAs (requires a 
> similar mechanism).
>
> https://issues.dlang.org/show_bug.cgi?id=17881
> 

Ok, thanks. I'll push for it.

One thing, though, that boggles me; how does the GC know where 
each class instance start and what type it has when I the 
allocator constructs it using `emplace` in my Region? So that the 
GC knows which destructor to call where.

Furher, is it ok to use my allocator to allocate both pod, 
structs and classes? Or aren't allocators supposed to be used in 
that way?