Must ranges support `r1 = r2;`?

[ag0aep6g]

On 03/24/2018 10:57 PM, H. S. Teoh wrote:
> On Sat, Mar 24, 2018 at 10:44:35PM +0100, ag0aep6g via Digitalmars-d wrote:
[...]
>> Short version: With two `std.range.RefRange`s, `r1 = r2;` does not
>> what other Phobos code expects.
[...]
> Short answer: if r1=r2 is meant to save the current position in the
> range, that's wrong; it should be r1=r2.save instead.

`r1 = r2.save;` has the exact same problem. See the linked Bugzilla 
issue for details.