null allowing @safe code to do unsafe stuff.

[deadalnix]

Le 18/03/2012 16:30, Andrei Alexandrescu a écrit :
> On 3/18/12 10:19 AM, Timon Gehr wrote:
>> On 03/18/2012 04:15 PM, deadalnix wrote:
>>> Le 18/03/2012 15:24, Timon Gehr a écrit :
>>>> On 03/18/2012 02:54 PM, deadalnix wrote:
>>>>> Given a class, that would create a very large object
>>>>
>>>> This is the culprit.
>>>>
>>>>> if instantiated,
>>>>> and a null reference, you can access memory in « raw mode ». This is
>>>>> @safe D code, but really isn't.
>>>>>
>>>>> As solution, @safe code should insert tests for null reference, or
>>>>> should prevent null to be used.
>>>>
>>>> This is fighting symptoms.
>>>
>>> @safe is supposed to be a guarantee. And, even if it is bad practice, in
>>> this case we aren't able to ensure that these guarantee are respected.
>>>
>>> Given that, @safe doesn't guarantee anything. You may think that this
>>> isn't a problem, but, what is the point of @safe if it is unable to
>>> ensure anything ?
>>
>> No null checks are necessary as long as there is no class that would
>> create such a very large object.
>
> Yah, we need to insert a rule that prevents creating class objects
> larger than 64KB. Java has the same.
>
> Andrei

This is another solution. In this case, we have to ensure that the first 
64kb of the system are page protected to detect null pointer deference 
in druntime.