Safe mode in D?

[Maxim Fomin]

On Friday, 18 October 2013 at 09:10:30 UTC, John Colvin wrote:
> On Friday, 18 October 2013 at 06:26:51 UTC, Maxim Fomin wrote:
>> On Thursday, 17 October 2013 at 23:25:52 UTC, Meta wrote:
>>> On Thursday, 17 October 2013 at 23:18:21 UTC, DDD wrote:
>>>> I tried this code and the compiler allowed it (runtime I get 
>>>> object.Error: Access Violation). What am I doing wrong?
>>>>
>>>> Thanks I didn't notice
>>>>
>>>> @safe
>>>> import std.stdio;
>>>> class A {
>>>> 	int x  = 1;
>>>> }
>>>> @safe void main() {
>>>> 	A a;
>>>> 	a.x=9;
>>>> }
>>>
>>> This is more or less a different thing. SafeD doesn't 
>>> guarantee that your class references will not be null. Trying 
>>> to call a method on a null reference is perfectly valid in 
>>> SafeD. There's a pull request sitting in GitHub for a NotNull 
>>> type that should be reasonable good for ensuring that your 
>>> references are not null, but it hasn't been pulled yet.
>>
>> Actually on linux this will segfault so in general this is not 
>> safe across all platforms.
>
> It's still memory safe in the sense that it's guaranteed to not 
> stomp on anything -> no silent corruption.

Well, in some sence yes. The problem with dereferencing nulls is 
that behavior is different in linux and windows (i.e. non 
portable), but you can enable treating nulls as exception in 
linux if you use etc.linux.memoryerrors.

> I don't really think the distinction between an Error or a 
> segfault is the dividing line between safe and not safe. Both 
> are supposed to be (under 99.9% of circumstances) unrecoverable 
> errors.

Some errors are propagated as exceptions, some errors are handled 
like abort, so situation depends on type of the error. Users are 
not supposed to catch errors, but they still can, which makes 
situation is compilcated in general.

However, dereferencing null is tiny problem comparing to other 
issues in D's safity.