UDA and trait for non-GC managed pointers

[Basile B. via Digitalmars-d]

On Saturday, 15 October 2016 at 16:22:35 UTC, Nordlöw wrote:
> Is there a way to check if a pointer is supposed to point to 
> non-GC allocated memory? I presume not. This is needed to 
> prevent unnecessary calls to `GC.addRange` in containers with 
> elements of a type that in turn is a container-like struct with 
> non-GC allocated memory.
>
> If not, maybe we could tag those non-GC-mangaged pointers with 
> a UDA, preferrably `@nogc`, and then build a trait, say, 
> `hasGCIndirections` that doesn't include @nogc-pointers.
>
> What do you think?

I agree. We are several people to do it already. I've started to 
during last spring (see 
https://forum.dlang.org/post/ficbsdfokvbvslatmomr@forum.dlang.org).
So far I use "@NoGc" and "@TellGcRange" added.

"@NoGc" is like what you describe, but it also allows to annotate 
class instances and, very important: D builtin array !

"@TellGcRange" prints a diagnostic at compile time which allows 
to find which aggregate members force my equivalent of "make" 
(called "construct") to declare a GC range (it should even be a 
root actually...).

To be honest I find this system way more useful that the function 
attribute @nogc.
My trait is here 
(https://github.com/BBasile/iz/blob/master/import/iz/memory.d#L145) but it's quite similar to the one used in EMSI containers (with diagnostic added).