Implicit conversion of unique chars[] to string

[Per Nordlöw]

On Tuesday, 23 March 2021 at 01:07:15 UTC, Steven Schveighoffer 
wrote:
> And the answer is complex. You can't accept a const range, 
> because they don't work. The only way to have purity infer 
> uniqueness is to accept paramters that the result could not 
> have come from. Usually this means accepting const and 
> returning mutable.

How do we want this to work with and without the presence of 
`return` qualified parameters?