[your code here]

[Jos van Uden]

> S rot13(S)(S s) if (isSomeString!S) {
> return rot(s, 13);
> }
>
> S rot(S)(S s, int key) if (isSomeString!S) {
> auto r = new dchar[s.walkLength()];
>
> foreach (i, dchar c; s) {
> if (isLower(c))
> r[i] = ((c - 'a' + key) % 26 + 'a');
> else if (isUpper(c))
> r[i] = ((c - 'A' + key) % 26 + 'A');
> }
> return to!S(r);
> }

this is better

S rot13(S)(in S s) if (isSomeString!S) {
     return rot(s, 13);
}

S rot(S)(in S s, in int key) if (isSomeString!S) {
     auto r = new dchar[s.walkLength];

     foreach (i, dchar c; s) {
         if (std.ascii.isLower(c))
             c = ((c - 'a' + key) % 26 + 'a');
         else if (std.ascii.isUpper(c))
             c = ((c - 'A' + key) % 26 + 'A');
         r[i] = c;
     }
     return to!S(r);
}