An exegesis of Walter's reference counted slice

[Steven Schveighoffer via Digitalmars-d]

On 2/24/15 2:40 PM, Andrei Alexandrescu wrote:
> I modified Walter's sample code to this:
> http://dpaste.dzfl.pl/f3d854feede9. It uses malloc for both the array
> and the reference count, and also uses @trusted minimally. I inserted
> assert()s here and there to clarify the workings. Nothing big except for
> the careful use of @trusted.
>
> I'll use this as a basis of some exegesis.
>
> 1. The code is a bit more complicated than it should. Overall this is
> not a biggie; regular D users are not supposed to write reference
> counted slices casually. But I was bummed that e.g. I found no way to
> call emplace() @safe-ly.

I have no problem with underlying complexity of primitive types. Using 
Objective-C objects is just fine without understanding the implementation.

Note, you need to GC.addRange all the elements if the type has 
references, or else you cannot have GC pointers in the array. For 
example, an array of class references could potentially result in those 
references being collected before the array is gone.

Ironically, if those elements are references, but are reference counted 
references, then you wouldn't need to addRange. An interesting problem...

> 2. Michel's point (https://issues.dlang.org/show_bug.cgi?id=14221)
> reveals the largest issue with RC/GC integration. We need to find a fix
> for it if we want to have the GC lift cycles.

I think a system of making sure a piece of data is always destroyed in 
the same thread it was created (unless of course, the thread is gone, in 
which case it doesn't matter), should be fine.

-Steve