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digitalmars.D.learn - weak_ptr alternative

reply Kamil Koczurek <koczurekk gmail.com> writes:
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.
Aug 05 2018
parent reply aliak <something something.com> writes:
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.
Aug 05 2018
parent Kamil Koczurek <koczurekk gmail.com> writes:
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.
Aug 05 2018