How is chunkBy supposed to behave on copy

[Dukc]

On Thursday, 19 March 2020 at 14:46:39 UTC, Steven Schveighoffer 
wrote:
> The only way to "fix" this IMO is to migrate to a system where 
> standard (non-forward) input ranges are not copyable, and 
> deprecate save. It likely will never happen.
>
> -Steve

Perhaps there is another way. Individual ranges can give 
guarantees about their own copy behaviour if they want. We could 
document the current copy behaviour of existing Phobos ranges and 
say that relying on it is thereafter fine.

But then the question with `chunkBy` is, should it take the 
opportunity to start to behave like most other ranges in this 
regard?