On 12/09/2014 08:53 AM, Steven Schveighoffer wrote:
> On 12/9/14 11:17 AM, ketmar via Digitalmars-d-learn wrote:
>> that file can be already finalized. please remember that `~this()` is
>> more a finalizer than destructor, and it's called on *dead* object.
Agreed: D has a terminology issue here, what we call a "class
destructor" is a "class finalizer". I have added D to the Wikipedia article:
http://en.wikipedia.org/wiki/Finalizer
Now I want to improve some of my chapters.
>> here this means that any other object in your object (including
>> structs) can be already finalized at the time GC decides to call your
>> finalizer.
Although I know the fact above, I think ketmar makes a distinction (that
is new to me) that a finalizer is a function that does not reference
class members but a destructor does (or safely can).
> File is specially designed (although it's not perfect) to be able to
> close in the GC. Its ref-counted payload is placed on the C heap to
> allow access during finalization.
>
> That being said, you actually don't need to write the above in the class
> finalizer, _file's destructor will automatically be called.
>
>> just avoid "destructors" unless you *really* need that. in your case
>> simply let GC finalize your File, don't try to help GC. this is not C++
>> (or any other language without GC) and "destructors" aren't destructing
>> anything at all. "destructors" must clean up the things that GC cannot
>> (malloc()'ed memory, for example), and nothing else.
>>
>
> Good advice ;)
>
> I would say other than library writers, nobody should ever write a class
> dtor.
>
> -Steve
Can somebody elaborate on that guideline please. Given a case where
runtime polymorphism is needed, so that we have to use classes, does the
guideline simply mean that "arrange for manual cleanup" or is there more
in that guideline? I am confused about the "library writers" part. :)
Thank you,
Ali
