Struct with default ctor (Was: [dmd-beta] dmd 2.064 beta take 2)

[deadalnix]

On Sunday, 19 May 2013 at 19:15:47 UTC, Andrei Alexandrescu wrote:
> Oh, the good old "object of sufficient size". We know how to 
> fix that.
>
>> And no, putting nullcheck on access of field of sufficient 
>> offset (as
>> propose dby Andrei) isn't enough because we have value types. 
>> Consider :
>>
>> S[BIG_NUMBER]* a;
>> auto s = &(*a[SLIGHTLY_BELLOW_CHECK_OFFSET]);
>> s.fieldAccess; // May not have enough offset to trigget null 
>> check, but
>> still can be usnafe
>>
>> See bug reports :
>> http://d.puremagic.com/issues/show_bug.cgi?id=3677
>> http://d.puremagic.com/issues/show_bug.cgi?id=5176
>
> All of the above are variations on the "sufficiently large 
> object" theme.
>
> Andrei

The code above never access a field with a sufficient offset to 
trigger "sufficiently large runtime check". Obviously, in the 
presented code the bug is trivial, but if the dereferences occurs 
across several functions, this is doomed to fail.

The solutions are : prevent any conglomerate of value type to be 
bigger than 4kb (the protection on OSX is 4kb) or put a null 
check on every dereference in @safe code.