std.algorithm.splitter on a string not always bidirectional

[Steven Schveighoffer]

On 1/22/21 2:56 PM, H. S. Teoh wrote:
> On Friday, 22 January 2021 at 17:29:08 UTC, Steven Schveighoffer wrote:
>> On 1/22/21 11:57 AM, Jon Degenhardt wrote:
> [...]
>>> Another way to look at it: If split (eager) took a predicate, that 
>>> 'xyz.splitter(args).back' and 'xyz.split(args).back' should produce 
>>> the same result. But they will not with the example given.
>>
>> With what example given? The example you gave is incomplete (what are 
>> args?)
> [...]
> 
> Here is a case for which iterating forwards yields a different sequence
> from iterating backwards (if we were to allow the latter):
> 
>      "bbcbcba".splitter("bcb")
> 
> Iterating forwards gives us the subranges: "b", "cba".
> 
> Iterating backwards gives us: "a", "bbc".
> 
> So it cannot be a bidirectional range, at least not in the expected sense
> that iterating from the back ought to give us the same subranges as
> iterating from the front, only in a reverse order.  Here iterating
> backwards yields a completely different decomposition.

Yes thank you! That makes sense, and I wasn't thinking of that.

I still believe that any splitter based on individual elements should be 
bidirectional.

-Steve