RC buffer

[Andrei Alexandrescu via Digitalmars-d]

On 11/02/2016 07:29 AM, Nick Treleaven wrote:
> On Wednesday, 2 November 2016 at 05:00:23 UTC, Andrei Alexandrescu wrote:
>> In order to make opAssign safe, a language change will be necessary.
>
> Technically, it should be possible with runtime checks:
>
> https://forum.dlang.org/post/aeeffshzkfjbrejztksj@forum.dlang.org
>
> The checking overheads disappear when -noboundschecks is passed. The
> user has to manually copy the RCSlice when necessary for correct code.

It seems opAssign for RCSlice is unsafe, is that right? Consider (with 
your codebase):

@safe void fun(ref RCSlice!int a, ref RCSlice!int b)
{
     a = RCSlice!int();
     ... use b ...
}

@safe void gun(ref RCSlice!int s)
{
     fun(s, s);
}

Assume the reference count of s is 1 upon entering gun. Then the first 
thing opAssign does is to call the destructor of the slice, which 
deallocates memory. Subsequently the other reference (b) is dangling.


Andrei