clear()

[Vladimir Panteleev]

On Fri, 09 Oct 2009 22:01:30 +0300, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> Andrei Alexandrescu wrote:
>> Jacob Carlborg wrote:
>>> On 10/9/09 18:40, Andrei Alexandrescu wrote:
>>>> I'm talking with Sean and Walter about taking the first step towards
>>>> eliminating delete: defining function clear() that clears the state of
>>>> an object. Let me know of what you think.
>>>>
>>>> One problem I encountered is that I can't distinguish between a  
>>>> default
>>>> constructor that doesn't need to exist, and one that was disabled
>>>> because of other constructors. Consider:
>>>>
>>>> class A {}
>>>> class B { this(int) {} }
>>>>
>>>> You can evaluate "new A" but not "new B". So it's legit to create
>>>> objects of type A all default-initialized. But the pointer to
>>>> constructor stored in A.classinfo is null, same as B.
>>>>
>>>> Any ideas?
>>>>
>>>>
>>>> Andrei
>>>
>>> How about this:
>>>
>>> static if (is(typeof({
>>>         auto t = new T;
>>>     })))
>>  I'm in awe. Thanks, Jacob!!!
>>  Andrei
>
> Oh, wait, that doesn't work:
>
> class A {}
> class B : A { this(int) {} }
>
> A a = new B;
> clear(a); // oops

 From what I understand, if you need to be able to look at derived classes,  
then this information can only be stored in the ClassInfo - but, as you  
have already pointed out, defaultConstructor is only set for explicit  
constructors. Therefore you'll need some kind of new flag, which indicates  
whether the class only has non-default constructors.

P.S. I hope that by "eliminating delete" you mean obsoleting it, and not  
actually taking it out of the language :)

-- 
Best regards,
  Vladimir                          mailto:thecybershadow at gmail.com