file rawRead and rawWrite in chunks example

[Ali Çehreli via Digitalmars-d-learn]

On 08/08/2015 04:11 PM, Jay Norwood wrote:
> I'm playing around with the range based operations and with raw file
> io.  I couldn't figure out a way to get rid of the outer foreach loops.

When the body of the foreach loop performs something, then 
std.algorithm.each can be useful:

import std.algorithm;
import std.stdio;
import std.range;
import std.datetime;

void main()
{

     auto fn = "numberList.db";

     std.datetime.StopWatch sw;
     sw.start();

     scope(exit) std.file.remove(fn);

     {
         auto f = File(fn,"wb");

         iota(10.5, 20_000_010.5, 1.0)
             .chunks(1000000)
             .each!(a => f.rawWrite(a.array));
     }

     {
         auto f = File(fn,"rb");

         const int n = 1000000;

         // NOTE: D-style syntax on the left-hand side
         double[] dbv = new double[n];

         // NOTE: No need to tell rawRead the type as double
         iota(10, 20_000_000 + 10, n)
             .each!(a => f.rawRead(dbv));
     }

     long tm = sw.peek().msecs;
     writeln("time msecs:", tm);
}

Ali