rvalues -> ref (yup... again!)

[John Colvin]

On Monday, 26 March 2018 at 14:40:03 UTC, Atila Neves wrote:
> On Friday, 23 March 2018 at 22:01:44 UTC, Manu wrote:
>> Forked from the x^^y thread...
>> <snip>
>
> There are too many replies on this thread, addressing all the 
> comments would take forever and pollute the thread itself. So 
> forgive me if I say something that was covered already by 
> someone else.
>
> AFAIK being able to bind rvalues to `ref const(T)`, only makes 
> sense when calling C++ functions that take `const T&` 
> (especially since that is common). I have not yet heard any 
> other use for them. I'd be in favour of allowing it _only_ for 
> `extern(C++)` functions. Otherwise use `auto ref` or have 
> overloads for pass-by-value and pass-by-ref.
> I too, once a recent immigrant from the lands of C++, used to 
> keep writing `ref const(T)`. I just pass by value now.
>
> C++ T&& (forwarding reference) -> D auto ref T
> C++ T&& (Rvalue reference) -> D T
> C++ const T& -> D T
> C++ T& -> D ref T
>
> If replacing const T& with T chafes, I understand. I used to 
> feel that way too. It's _possible_ that would incur a penalty 
> in copying/moving, but IME the cost is either 0, negligible, or 
> negative (!).

I'm tearing my remaining stubs of hair out trying to understand 
why memory copies (not talking about copy constructors) are 
needed when passing an rvalue to a non-ref function: 
https://stackoverflow.com/questions/49474685/passing-rvalue-to-non-ref-parameter-why-cant-the-compiler-elide-the-copy