RFC on range design for D2

[Andrei Alexandrescu]

bearophile wrote:
> Few benchmarks, appending ints, note this is a worst-case situation (other benchmarks are less dramatic). Just many appends, followed by the "release":
> 
> benchmark 10, N=10_000_000:
>   Array append:  0.813 s
>   ArrayBuilder:  0.159 s
>   ArrayAppender: 1.056 s
> 
> benchmark 10, N=100_000_000:
>   Array append:  10.887 s
>   ArrayBuilder:   1.477 s
>   ArrayAppender: 13.305 s

That's odd. The array appender should never, by definition, do 
significantly worse than the straight array append. I think some other 
factor intervened (e.g. swapping). Also don't forget to compile with -O 
-release -inline and to test several times after a warmup run. I adapted 
your code obtaining the numbers below:

benchmark 10, N=10000000:
   Array append: 0.69 s
   ArrayAppender: 0.19 s

benchmark 10, N=25000000:
   Array append: 2.06 s
   ArrayAppender: 0.82 s

benchmark 10, N=50000000:
   Array append: 4.28 s
   ArrayAppender: 1.75 s

benchmark 10, N=75000000:
   Array append: 9.62 s
   ArrayAppender: 5.8 s

benchmark 10, N=100000000:
   Array append: 11.35 s
   ArrayAppender: 6.20 s


Andrei