Should this invariant always hold? equal(range.retro.array, range.array.retro)

[Dukc]

On Monday, 17 October 2022 at 11:02:07 UTC, FeepingCreature wrote:
> Trolling a bit: Should this invariant always hold?
>
> assert(equal(range.retro.array, range.array.retro));

Posting this without having looked at other replies.

No. The range could be a reference range, in which case this does 
not hold unless the range is already empty.

The invariant would have to be 
`assert(equal(range.save.retro.array, range.save.array.retro));` 
instead.

Also this won't hold if the range contains floating point NaNs, 
or other elements that are not equal to themselves.

There may be other corner cases too I didn't think of.