Null references redux

[Andrei Alexandrescu]

downs wrote:
> Walter Bright wrote:
>> Nick Sabalausky wrote:
>>
>> I agree with you that if the compiler can detect null dereferences at
>> compile time, it should.
>>
>>
>>>> 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.
>>> No, he's using the real meaning of "safe", not the
>>> misleadingly-limited "SafeD" version of "safe" (which I'm still
>>> convinced is going to get some poor soul into serious trouble from
>>> mistakingly thinking their SafeD program is much safer than it really
>>> is). Out here in reality, "safe" also means a lack of ability to
>>> crash, or at least some level of protection against it. 
>> Memory safety is something that can be guaranteed (presuming the
>> compiler is correctly implemented). There is no way to guarantee that a
>> non-trivial program cannot crash. It's the old halting problem.
>>
> 
> Okay, I'm gonna have to call you out on this one because it's simply incorrect.
> 
> The halting problem deals with a valid program state - halting.
> 
> We cannot check if every program halts because halting is an instruction that must be allowed at almost any point in the program.
> 
> Why do crashes have to be allowed? They're not an allowed instruction!
> 
> A compiler can be turing complete and still not allow crashes. There is nothing wrong with this, and it has *nothing* to do with the halting problem.
> 
>>> You seem to be under the impression that nothing can be made
>>> uncrashable without introducing the possibility of corrupted state.
>>> That's hogwash.
>> I read that statement several times and I still don't understand what it
>> means.
>>
>> BTW, hardware null pointer checking is a safety feature, just like array
>> bounds checking is.
> 
> PS: You can't convert segfaults into exceptions under Linux, as far as I know.

How did Jeremie do that?

Andrei