On Iteration

[Bill Baxter]

On Tue, Nov 10, 2009 at 11:34 AM, Phil Deets <pjdeets2 at gmail.com> wrote:
> On Tue, 10 Nov 2009 05:18:59 -0500, Lutger <lutger.blijdestijn at gmail.com>
> wrote:
>
>> - why is a UTF-string iterator bidirectional and why is that unexpected?
>
> I think it is wouldn't support random access since accessing the nth code
> point (code points are similar to characters) is not a constant time
> operation since different code points can be made up of different numbers of
> bytes. That isn't necessarily intuitive since UTF-strings are stored
> contiguously in memory; so you might expect them to be random-accessible.

I thought the comment was about this:  you might expect it to be just
a forward iterator, but (surprise!) you can also find the previous
codepoint in O(1) time, due to lead units being in values ranges
distinct from following units.  But I still don't find it particularly
unexpected.  It's probably only unexpected if you don't know anything
about UTF other than the fact that each character is a variable number
of bytes.

--bb