RCArray is unsafe

[Zach the Mystic via Digitalmars-d]

On Wednesday, 4 March 2015 at 19:22:25 UTC, Zach the Mystic wrote:
> On Wednesday, 4 March 2015 at 18:17:41 UTC, Andrei Alexandrescu 
> wrote:
>> 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.
>
> The third solution is to keep track of lifetimes, recognize 
> refcounted types for structs the same as suggested for classes 
> in DIP74, and wrap the lifetime of the subreference `t.s` in an 
> opAdd/Release cycle for `t`, as illustrated in my other reply. 
> You could have the compiler recognize a refcounted struct by 
> simply declaring "void opAddRef();" and "void opRelease();", 
> with the compiler automatically aliasing them to "this(this)" 
> and "~this".

I'm sorry, I just realized this proposal is too complicated, and 
it wouldn't even work.

I think stricter static checking in @safe code is the way to go. 
When passing a global RC type to an impure, or duplicating the 
same RC reference variable in a function call, it's unsafe. The 
workaround is to make copies and use them:

static RcType s; // global
RcType c;

// Instead of:
func(s);
func(c, c);

// ...do this:
auto tmp = s; // get stack reference
func(tmp);
auto d = c; // copy Rc'd type
func(c, d);

Expensive, perhaps, but safe.