retro() on a `string` creates a range of `dchar`, causing array() pains

[Ali Çehreli]

On 04/17/2012 09:12 AM, Timon Gehr wrote:
 > On 04/17/2012 06:09 PM, Ali Çehreli wrote:

 >> The algorithm must be building a local string.

 > It does not have to build a local string, see
 > http://dlang.org/phobos/std_utf.html#strideBack

I never said otherwise. :p

I was too lazy to locate where 2.059's algorithm.d was placed under. 
Apparently it is here:

   /usr/include/x86_64-linux-gnu/dmd/phobos/std/algorithm.d

The algorithm is smart. It reverses individual Unicode characters 
in-place first and then reverses the whole string one last time:

void reverse(Char)(Char[] s)
if (isNarrowString!(Char[]) && !is(Char == const) && !is(Char == immutable))
{
     auto r = representation(s);
     for (size_t i = 0; i < s.length; )
     {
         immutable step = std.utf.stride(s, i);
         if (step > 1)
         {
             .reverse(r[i .. i + step]);
             i += step;
         }
         else
         {
             ++i;
         }
     }
     reverse(r);
}

Ali

P.S. Being a C++ programmer, exception-safety is always warm in my mind. 
Unfortunately the topic does not come up much in D forums. The algorithm 
above is not exception-safe because stride() may throw. But this way off 
topic on this thread. :)