Is there a way to keep track of objects without owning them? That is, could I have a smart pointer that behaves somewhat like this:

WeakPtr!Class wptr = getSomeInstance();
auto obj = wptr.peek; //[1]
if(obj !is null) {
  obj.stuff();
}

[1]: If wptr points to something that is still reachable from somewhere else (and wasn't yet marked for collection by GC), .peek would return a normal reference of type Class. OTOH, when no active reference is present it should return null.

On Sunday, 5 August 2018 at 20:10:49 UTC, Kamil Koczurek wrote:
> Is there a way to keep track of objects without owning them? That is, could I have a smart pointer that behaves somewhat like this:
>
> WeakPtr!Class wptr = getSomeInstance();
> auto obj = wptr.peek; //[1]
> if(obj !is null) {
>   obj.stuff();
> }
>
> [1]: If wptr points to something that is still reachable from somewhere else (and wasn't yet marked for collection by GC), .peek would return a normal reference of type Class. OTOH, when no active reference is present it should return null.

Not sure if there's anything in the language or standard library, but there this:

https://github.com/w0rp/dstruct/blob/master/source/dstruct/weak_reference.d

Which admittedly I have not tested.

On Sunday, 5 August 2018 at 20:57:32 UTC, aliak wrote:
> On Sunday, 5 August 2018 at 20:10:49 UTC, Kamil Koczurek wrote:
>> Is there a way to keep track of objects without owning them? That is, could I have a smart pointer that behaves somewhat like this:
>>
>> WeakPtr!Class wptr = getSomeInstance();
>> auto obj = wptr.peek; //[1]
>> if(obj !is null) {
>>   obj.stuff();
>> }
>>
>> [1]: If wptr points to something that is still reachable from somewhere else (and wasn't yet marked for collection by GC), .peek would return a normal reference of type Class. OTOH, when no active reference is present it should return null.
>
> Not sure if there's anything in the language or standard library, but there this:
>
> https://github.com/w0rp/dstruct/blob/master/source/dstruct/weak_reference.d
>
> Which admittedly I have not tested.

Not exactly what I want, in my case the pointer should become null when all other instances go out of reach, not when they're collected, which isn't really predictable in D AFAIK. I can't base logic of my program on this.

Still interesting though, I'll look into its implementation and docs on core.memory, maybe I'll manage to implement it by myself.