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digitalmars.D.learn - Handling referencing class parent instances in a GC friendly way.

reply realhet <real_het hotmail.com> writes:
Hi,

class A{
   A parent;
   A[] items;

   void myDestroy(){
     items.each!(i => i.myDestroy);
     parent = null;
     // after this point I think the GC will release it 
automatically, and it will call ~this() too. Am I right?
   }
}

I have a hierarchy of class instances forward and backward linked 
to its items ant its parent.

What is a proper way to destroy an instance of class A? Is 
calling instance.myDestroy sufficient?

Am I right that this kind of uninitialization MUST not go into 
the ~this() destructor, because of the references the instance is 
holding, the system will never call the ~this()?

Or is there a better way for this type of thing in Dlang?


Thanks in advance!
Nov 30 2020
parent reply FeepingCreature <feepingcreature gmail.com> writes:
On Monday, 30 November 2020 at 14:33:22 UTC, realhet wrote:

 Hi,

 class A{
   A parent;
   A[] items;

   void myDestroy(){
     items.each!(i => i.myDestroy);
     parent = null;
     // after this point I think the GC will release it 
 automatically, and it will call ~this() too. Am I right?
   }
 }

 I have a hierarchy of class instances forward and backward 
 linked to its items ant its parent.

 What is a proper way to destroy an instance of class A? Is 
 calling instance.myDestroy sufficient?

 Am I right that this kind of uninitialization MUST not go into 
 the ~this() destructor, because of the references the instance 
 is holding, the system will never call the ~this()?

 Or is there a better way for this type of thing in Dlang?


 Thanks in advance!


The GC will release it anyways. The advantage of a GC is that it 
is not deterred by cyclic references, so as soon as no more 
references into A exist, it will disappear, no matter the parent 
pointer.

At least, that's the theory - in practice, since we don't have 
precise stack GC, any spurious or leftover pointer to an A can 
keep the whole tree alive, so the myDestroy cleanup method is 
still valid and recommended. Though you may want to do `items = 
null;` too.
Nov 30 2020
parent realhet <real_het hotmail.com> writes:
On Monday, 30 November 2020 at 14:36:08 UTC, FeepingCreature 
wrote:

 On Monday, 30 November 2020 at 14:33:22 UTC, realhet wrote:
 ...
 Though you may want to do `items = null;` too.


I just forgot 1 of three things, thx for pointing it out.
And I also forget to notify the parent to remove the reference 
from its items list.
Nov 30 2020