DIP 1016--ref T accepts r-values--Formal Assessment

[Dominikus Dittes Scherkl]

On Monday, 4 February 2019 at 17:09:25 UTC, bitwise wrote:

> I think this solves all of the above:
>
> fun(10);
> ==>
> (int __temp0){ (return)? fun( __temp0 ); }(10);
>
> -The expression/statement issue is solved by the closure
> -The initialization issue created by the ":=" approach is not 
> present here
> -For this rewrite, 'T' is the type of the rvalue argument, not 
> the type of the function parameter. This prevents undesired 
> implicit conversions.

I don't understand this.
What does "(return)?" mean? Is this valid D syntax? What do I 
miss?