DIP77 - Fix unsafe RC pass by 'ref'

[Walter Bright via Digitalmars-d]

On 4/10/2015 2:20 PM, Martin Nowak wrote:
> On 04/10/2015 12:29 PM, Walter Bright wrote:
>>>
>>> So someone passes an RCO via ref to avoid the inc/dec, and because
>>> that imposes
>>> safety issues we turn it into some sort of pass by value under the hood,
>>> defeating the purpose, and provide an opt-out via @system opAssign.
>>
>> Or you could pass it by const ref (which is what Rust essentially does).
>
> Maybe I'm missing something, but this proposal seems to make `ref RCO`
> fairly useless, because it creates a copy anyhow.

Not if you read the copy elision section.


> Assigning a RefCounted is marked @system,

That's kind of throwing in the towel, isn't it?

> pass-by-ref is @safe.
> What's missing, you want to be able to use RefCounted in @safe code? Why
> not pass it by value then? That would pin the object and you could elide
> the additional inc/dec just like you propose to elide the temporary copies.
> It's more efficient to pass a smart pointer like RefCounted by-value anyhow.