RCArray is unsafe

weaselcat via Digitalmars-d digitalmars-d at puremagic.com
Mon Mar 2 15:47:55 PST 2015

On Monday, 2 March 2015 at 22:51:03 UTC, Walter Bright wrote:
> On 3/2/2015 1:12 PM, deadalnix wrote:
>> I do think you are confusing how Rust does it. In Rust, 
>> borrowing makes the
>> source and borrowed reference immutable by default. So by 
>> default the problem do
>> not occurs.
> May I refer you to:
> http://static.rust-lang.org/doc/0.6/tutorial-borrowed-ptr.html#borrowing-managed-boxes-and-rooting
> "Again the lifetime of y is L, the remainder of the function 
> body. But there is a crucial difference: suppose x were to be 
> reassigned during the lifetime L? If the compiler isn't 
> careful, the managed box could become unrooted, and would 
> therefore be subject to garbage collection. A heap box that is 
> unrooted is one such that no pointer values in the heap point 
> to it. It would violate memory safety for the box that was 
> originally assigned to x to be garbage-collected, since a 
> non-heap pointer---y---still points into it.
> [...]
> For this reason, whenever an & expression borrows the interior 
> of a managed box stored in a mutable location, the compiler 
> inserts a temporary that ensures that the managed box remains 
> live for the entire lifetime. [...] This process is called 
> rooting."
> It's possible that this is an old and obsolete document, but 
> it's what I found.

That's actually very old(0.6 - nearly 2 years ago.) I believe 
rooting was dropped from the language completely.


also, rust by example chapter 17-19 cover this

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