Look and think good things about D

[bearophile]

Ary Borenszweig:

> And so LLVM, which is what Crystal uses as a backend.

LDC2 uses the same back end :-)


> But I thought ranges were meant to be fast. No allocations and 
> all of that. In fact, I was kind of sad that Crystal doesn't 
> have a similar concept so it could never get as fast as D 
> ranges. But if D ranges are not fast, what's the point of 
> having them and making everyone use them?

If you use ranges badly you will get a slow program, if you use 
them well with a good back-end, you will have a fast program.

I have written a third intermediate program, it's longer than 
yours, and it seems much slower than your code:


void main(in string[] args) {
     import std.stdio, std.conv, std.algorithm, std.array;

     immutable n = (args.length == 2) ? args[1].to!uint : 10;
     if (n == 0)
         return;

     auto seq = "1";
     writefln("%2d: n. digits: %d", 1, seq.length);
     foreach (immutable i; 2 .. n + 1) {
         Appender!string result;
         foreach (immutable digit, immutable count; seq.group) {
             result ~= "123"[count - 1];
             result ~= digit;
         }
         seq = result.data;
         writefln("%2d: n. digits: %d", i, seq.length);
     }
}


On my system it runs in 0.34 seconds for n=50. Could you compare 
some of the timings of the various D/Crystal versions on your 
system (using ldc2 for D)?

Bye,
bearophile