References in D

[Alex Burton]

On Thursday, 4 October 2012 at 17:55:45 UTC, Jonathan M Davis 
wrote:
> On Thursday, October 04, 2012 13:14:00 Alex Burton, @gmail.com 
> wrote:
>> On Saturday, 15 September 2012 at 21:30:03 UTC, Walter Bright
>> 
>> wrote:
>> > On 9/15/2012 5:39 AM, Henning Pohl wrote:
>> >> The way D is dealing with classes reminds me of pointers
>> >> because you can null
>> >> them. C++'s references cannot (of course you can do some 
>> >> nasty
>> >> casting).
>> > 
>> > Doing null references in C++ is simple:
>> > 
>> > int *p = NULL;
>> > int& r = *p;
>> > 
>> > r = 3; // crash
>> 
>> IMHO int * p = NULL is a violation of the type system and 
>> should
>> not compile.
>> NULL can in no way be considered a pointer to an int.
>
> Um. What? It's perfectly legal for pointers to be null. The 
> fact that *p
> doesn't blow up is a bit annoying, but it makes sense from an 
> implementation
> standpoint and doesn't really cost you anything other than a 
> bit of locality
> between the bug and the crash.

I realise what is currently the case I am making an argument as 
to why I this should be changed (at least for class references in 
D).

>> In the same way this should fail:
>> Class A
>> {
>> 
>> }
>> A a;
>
> And why would this fail? It's also perfectly legal.

I realise that this is currently legal, I am proposing that it 
shouldn't be.

If I call a method on reference a (perhaps after it has been 
passed around to a different part of the code) I get an acess 
violation / segfault whatever - Undefined behaviour.
On windows you might get stack unwinding, but otherwise not.
Failing with a memory violation is a bad thing - much worse than 
failing with an exception.
If I press a button in an app and it has a memory violation I can 
loose all my work, and potentially leave parts of a system in 
undefined states , locks on things etc.
If I get an exception, and the code is exception safe, the gui 
can indicate that the button doesn't work right now - maybe 
saying why, and the user can continue without loosing all their 
stuff (hopefully not pressing the same button and finding the 
same bug).

Alex