[Issue 16210] std.utf.byUTF can be made into a bidirectional range

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16210

--- Comment #2 from Jack Stouffer <jack at jackstouffer.com> ---
(In reply to Jakub Łabaj from comment #1)
> Assuming "ö" == [0xC3, 0xB6], which one version would be correct:
> a) behaviour of std.utf.byCodeUnit, just go by code units backward:
> "ö".byUTF!char().back == 0xB6
> 
> b) decode the character and return its first code unit:
> "ö".byUTF!char().back == 0xC3
> 
> Personally I thought the b) version is desired (docs says that byUTF encodes
> input), but at the moment it passes some inputs to byCodeUnit - it means for
> some ranges byUTF is bidirectional already and version a) applies.

Well damn. IMO B is more intuitive in all situations, so byUTF returning by
byCodeUnit isn't want we really want.

But because we can't break code, we would have to have B be the behavior only
when some encoding has to be done inside of byUTF and clearly document this odd
behavior.

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