Is the `in` operator @safe?

[Simen Kjærås]

On Monday, 11 February 2019 at 21:47:05 UTC, Luís Marques wrote:
> After a quick look it seems like the `in` operator may return a 
> pointer that becomes invalid when an AA is resized:
>
> https://github.com/dlang/druntime/blob/master/src/rt/aaA.d#L601
> https://github.com/dlang/druntime/blob/master/src/rt/aaA.d#L114
> https://github.com/dlang/druntime/blob/master/src/rt/aaA.d#L193
>
> Yet you can use `in` in @safe functions and keep the pointer 
> around. Is my assessment correct, or did I overlook anything? 
> If so, I'll open a bug report (I didn't find one already open 
> for that, but maybe I searched the wrong keywords).

This quick test indicates that the pointer doesn't get 
invalidated:

@safe unittest {
     import std.stdio : writeln;
     int[int] arr;
     arr[0] = 0;
     int* p = 0 in arr;
     int n = 1;
     while (p == (0 in arr)) {
         if (n % 1000 == 0) n.writeln;
         arr[n++] = 0;
     }
     n.writeln;
}

It crashes with an OutOfMemoryError after allocating ~27M 
elements on my machine.

It seems the AA is actually holding a list of Buckets, with each 
bucket containing a pointer to the actual element. When it's 
resize only the bucket list is affected, and the element pointers 
are still valid.

--
   Simen