Null references redux

[Max Samukha]

Lionello Lunesu wrote:

> On 27-9-2009 9:20, Walter Bright wrote:
>> language_fan wrote:
>>> The idea behind non-nullable types and other contracts is to catch
>>> these errors on compile time. Sure, the code is a bit harder to write,
>>> but it is safe and never segfaults. The idea is to minimize the amount
>>> of runtime errors of all sorts. That's also how other features of
>>> statically typed languages work.
>>
>>
>> I certainly agree that catching errors at compile time is preferable by
>> far. Where I disagree is the notion that non-nullable types achieve
>> this. I've argued extensively here that they hide errors, not fix them.
>>
>> Also, by "safe" I presume you mean "memory safe" which means free of
>> memory corruption. Null pointer exceptions are memory safe. A null
>> pointer could be caused by memory corruption, but it cannot *cause*
>> memory corruption.
> 
> // t.d
> void main()
> {
>     int* a;
>     a[20000] = 2;
> }
> 
> [C:\Users\Lionello] dmd -run t.d
> 
> [C:\Users\Lionello]
> 
> This code passes on Vista. Granted, needs a big enough offset and some
> luck, but indexing null will never be secure in the current flat memory
> models.
> 
> L.

That is a strong argument. If an object is big enough, modifying it via a 
null reference may still cause memory corruption. Initializing references to 
null does not guarantee memory safety.