DIP77 - Fix unsafe RC pass by 'ref'

[deadalnix via Digitalmars-d]

On Friday, 10 April 2015 at 10:02:01 UTC, Martin Nowak wrote:
> On Wednesday, 8 April 2015 at 23:11:08 UTC, Walter Bright wrote:
>> http://wiki.dlang.org/DIP77
>
> 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.
>
> Wouldn't it more straightforward to make pass-by-ref unsafe 
> (@system) for RCOs?
>
> Then the only thing missing to make this equally powerful, 
> would be an optimization opportunity for the compiler to elide 
> copies of pass-by-value RCOs, e.g. it could avoid calling the 
> postblit when the function retains the refcount.

Only the first pass by ref create a copy. You can then pass the 
ref down all you want without copy.

That is an acceptable cost IMO.