RCArray is unsafe
Andrei Alexandrescu via Digitalmars-d
digitalmars-d at puremagic.com
Wed Mar 4 10:17:41 PST 2015
On 3/4/15 9:22 AM, Steven Schveighoffer wrote:
> On 3/4/15 10:42 AM, Andrei Alexandrescu wrote:
>> On 3/4/15 12:55 AM, Ivan Timokhin wrote:
>>> Excuse me if I miss something obvious, but:
>>> void main()
>>> auto arr = RCArray!int();
>>> foo(arr, arr);
>>> void foo(ref RCArray!int arr, ref int val)
>>> auto copy = arr; //arr's (and copy's) reference counts
>>> are both 2
>>> arr = RCArray!int(); // There is another owner, so arr
>>> // forgets about the old payload
>>> } // Last owner of the array ('copy') gets destroyed and
>>> // frees the payload.
>>> val = 3; // Oops.
>> That's a problem, thanks very much for pointing it out. -- Andrei
> Again, I think this is an issue with the expectation of RCArray. You
> cannot *save* a ref to an array element, only a ref to the array itself,
> because you lose control over the reference count.
> I don't think arr should correctly bind to foo's second argument.
Yah, this is a fork in the road: either we solve this with DIP25 +
implementation, or we add stricter static checking disallowing two lent
references to data in the same scope.
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