Disallow null references in safe code?

[Walter Bright]

On 2/1/2014 12:09 PM, Andrei Alexandrescu wrote:
> On 2/1/14, 2:14 AM, Jonathan M Davis wrote:
>> How is it unsafe? It will segfault and kill your program, not corrupt memory.
>> It can't even read any memory. It's a bug to dereference a null pointer or
>> reference, but it's not unsafe, because it can't access _any_ memory, let
>> alone memory that it's not supposed to be accessing, which is precisely what
>> @safe is all about.
>
> This has been discussed to death a number of times. A field access obj.field
> will use addressing with a constant offset. If that offset is larger than the
> lowest address allowed to the application, unsafety may occur.
>
> The amount of low-address memory protected is OS-dependent. 4KB can virtually
> always be counted on. For fields placed beyond than that limit, a runtime test
> must be inserted. There are few enough 4KB objects out there to make this
> practically a non-issue. But the checks must be there.

Another way to deal with it is to simply disallow @safe objects that are larger 
than 4K (or whatever the size is on the target system).