Binding rvalues to ref parameters redux

[Nicholas Wilson]

On Thursday, 28 March 2019 at 14:36:59 UTC, bitwise wrote:
> On Wednesday, 27 March 2019 at 01:38:40 UTC, Andrei 
> Alexandrescu wrote:
>> Here, the DIP Author clearly expresses two reasons why a 
>> programmer may choose to declare a function to accept `ref` 
>> arguments. The Language Maintainers see this as the core of 
>> the proposal and would expect the distinction between the two 
>> cases to be maintained throughout. [However, this proposal 
>> does not maintain the distinction and instead conflates the 
>> two][1] cases. The Language Maintainers insist that any 
>> proposal allowing `ref` parameters to accept rvalue references 
>> must clearly define how functions which make use of `ref` for 
>> side effects will not accept rvalues.
>
> I don't see anything in the new DIP that addresses the above 
> issue. [1]

Thats because it was never an issue with the dip, the conflation 
was entirely deliberate, It is the review if the dip that was 
wrong. This issue is resolved by the fact that temporaries 
created are not usable after the expression they appear in, and 
things that look like lvalues (e.g. @property functions) are 
disallowed as candidates for rvalue -> ref conversion.

> It seems like a waste to have a keyword that's just an alias 
> for two others (in = const scope), so why not put 'in' to 
> better use, like to qualify a ref parameter as accepting 
> rvalues, or to outright replace 'ref' for rvalue-ref accepting 
> parameters?

Code breakage.