Function to print a diamond shape

[Jay Norwood]

> Interesting. I'd have thought the "extra copy" would be an 
> overall slowdown, but I guess that's not the case.


>
> I also tried your strategy of adding '\n' to the buffer, but I 
> was getting some bad output on windows. I'm not sure why "\n\n" 
> works though. On *nix, I'd have also expected a double line 
> feed. Did you check the actual output?

I checked the output.  The range selected is for one newline.
>
> Appender is better than "~=", but it's not actually that good 
> either. Try this:
>
> //----
> void printDiamond3(size_t N)
> {
>     import core.memory;
>     char* p = cast(char*)GC.malloc(N*N+16);
>     p[0..N*N+16]='*';
>
>     auto pp = p;
>     N/=2;
>     enum code = q{
>         pp[0 .. N - n] = ' ';
>         pp+=(1+N+n);
>         version(Windows)
>         {
>             pp[0 .. 2] = "\r\n";
>             pp+=2;
>         }
>         else
>         {
>             pp[0] = '\n';
>             ++pp;
>         }
>     };
>     foreach        (n; 0 .. N + 1) {mixin(code);}
>     foreach_reverse(n; 0 .. N    ) {mixin(code);}
>     write(p[0 .. pp-p]);
> }
> //----
>
> This makes just 1 allocation of roughly the right size. It also 
> eagerly fills the entire array with '*', since I *figure* 
> that's faster than a lot of different writes.
>
> I could be mistaken about that though, but I imagine the 
> pre-allocation and not using Appender is definitely a boost.

ok. I'll try it.  I was happy the appender was pretty fast.