How to write a proper class destructor?

[Bradley Smith]

Jarrett Billingsley wrote:
> "Bradley Smith" <digitalmars-com at baysmith.com> wrote in message 
> news:ep9joi$1mr2$1 at digitaldaemon.com...
>> According to the documentation, a class destructor is "expected to release 
>> any resources held by the object."[1] However, if resources to be released 
>> are in objects to be garbage collected, "those references are no longer 
>> valid."[1]
>>
>> How is a class supposed to release something for which it no longer has a 
>> valid reference?
> 
> Huuaaaahhh!
> 
> I remember someone suggesting that 'scope' be a valid modifier for class 
> instance variables, and it'd basically mean "when this class gets destroyed, 
> destroy this other instance as well."  Like auto-deletion when you use a 
> scope reference in a function:

Is scope a valid modifier for a data member? The documentation states 
"scope cannot be applied to globals, statics, data members, inout or out 
parameters".[2] In my tests, using scope on a data member compiles, but 
doesn't change the behavior.


> 
> class ResourceHolder
> {
>     scope SomeResource mRsrc;
> 
>     this(char[] name)
>     {
>         mRsrc = new SomeResource(name);
>     }
> }
> 
> ..
> 
> {
>     scope holder = new ResourceHolder("a.file");
>     ...
> } // holder is destroyed here, and so is its mRsrc member.
> 
> Another solution would be to change the behavior of the GC so that deletion 
> on program end _is_ deterministic.  That is, it'd basically run a collection 
> sweep, call finalizers on objects which don't have references to them, and 
> keep doing that until nothing is left.  That way, references to other 
> classes would always be valid in destructors, since the GC wouldn't collect 
> those references until everything that points to them is destroyed. 
> 

Are you saying that a proper class destructor can't be written without 
modifying the language?


Thanks,
   Bradley


[2] http://www.digitalmars.com/d/attribute.html#scope