[C++] String reverse kernel

[asfimport]

Like SQL reverse or Python 'string'[::-1]

Reporter: Ian Cook / @ianmcook
Assignee: Niranda Perera / @nirandaperera

Related issues:

• [C++] String algorithm library for StringArray/BinaryArray (is a child of)
• [R] Bindings for utf8_reverse and ascii_reverse (is depended upon by)

PRs and other links:

• GitHub Pull Request #10317

_{Note: This issue was originally created as ARROW-12713. Please see the migration documentation for further details.}

[asfimport]

Niranda Perera / @nirandaperera:
@ianmcook do you think it makes sense to extend 'reversing' to binary type as well?

[asfimport]

Ian Cook / @ianmcook:
@nirandaperera I'm not sure. Maybe it could be useful on bytes. I think the more important thing is that it handles UTF8 strings. (Or maybe there would be separate ascii_ and utf8_ functions.)

[asfimport]

Niranda Perera / @nirandaperera:
One thing I saw was, almost all the String kernels (utf8/ ascii) are only adding impls for StringType and LargeStringType types.

https://github.com/apache/arrow/blob/1a6e90c2b0872ad16df29c8f9d0a54154c1988d7/cpp/src/arrow/compute/kernels/scalar_string.cc#L2132

Was wondering if some of these should also add BinaryType kernels?

[asfimport]

Ian Cook / @ianmcook:
I think adding a binary kernel is much less important than adding the ascii and utf8 kernels. Others' opinions might vary. cc @jorisvandenbossche @pitrou

[asfimport]

Antoine Pitrou / @pitrou:
Adding a binary kernel is generally relatively cheap in termes of developer time. In any case, I don't really understand in which circumstances it's useful to reverse a string, so I won't comment on the usefulness of reversing binary data ;-)

[asfimport]

Ian Cook / @ianmcook:
A common reason for reversing a string is that some regular expression challenges are easier to solve if the string is reversed

[asfimport]

David Li / @lidavidm:
Issue resolved by pull request 10317
#10317