RCArray is unsafe

[Andrei Alexandrescu via Digitalmars-d]

On 3/4/15 2:03 AM, deadalnix wrote:
> A free list does not work as the data can be live. You cannot reuse it
> to maintain the free list.

Actually you can, which is a bit surprising. Consider:

RCArray!int arr;
arr.length = 10;
arr[5] = 42;
fun(arr, arr[5]);
...
void fun(ref RCArray!int a, ref int b) {
     assert(b == 42);
     a = a.init; // array goes to freelist
     a.length = 10; // array may reuse the previous one!
     assert(b == 42);
}

Now the interesting here thing is, the last assert should be allowed to 
fail. The code is still safe because there is no change of type, and the 
use of b after the array is gone is a bug in the application anyway 
because the parent structure is out of existence.

This makes code potentially tighter on memory usage but potentially more 
difficult to debug.


Andrei