C `restrict` keyword in D

[Johan Engelen via Digitalmars-d]

On Monday, 4 September 2017 at 21:23:50 UTC, Moritz Maxeiner 
wrote:
> On Monday, 4 September 2017 at 17:58:41 UTC, Johan Engelen 
> wrote:
>>
>> (The spec requires crashing on null dereferencing, but this 
>> spec bit is ignored by DMD and LDC, I assume in GDC too.
>> Crashing on `null` dereferencing requires a null-check on 
>> every dereferencing through an unchecked pointer, because 0 
>> might be a valid memory access, and also because 
>> ptr->someDataField is not going to lookup address 0, but 
>> 0+offsetof(someDataField) instead, e.g. potentially addressing 
>> a valid low address at 1000000, say.)
>
> It's not implemented as compiler checks because the "actual" 
> requirement is "the platform has to crash on null dereference" 
> (see the discussion in/around [1]). Essentially: "if your 
> platform doesn't crash on null dereference, don't use D on it 
> (at the very least not @safe D)".

My point was that that is not workable. The "null dereference" is 
a D language construct, not something that the machine is doing. 
It's ridiculous to specify that reading from address 1_000_000 
should crash the program, yet that is exactly what is specified 
by D when running this code (and thus null checks need to be 
injected in many places to be spec compliant):

```
struct S {
   ubyte[1_000_000] a;
   int b;
}
void main() {
    S* s = null;
    s.b = 1;
}
```

-Johan