How to remove all characters from a string, except the integers?

[matheus]

On Thursday, 3 March 2022 at 23:46:49 UTC, H. S. Teoh wrote:
> ...
> This version doesn't even allocate extra storage for the 
> filtered digits, since no storage is actually needed (each 
> digit is spooled directly to the output).

OK but there is another problem, I tested your version and mine 
and there is a HUGE difference in speed:

LDC 1.27.1, with -O2:

import std.datetime.stopwatch;
import std.stdio: write, writeln, writef, writefln;
import std;

void printStrTim(string s,StopWatch sw){
     writeln("\nstr: ", s
             ,"\nTim(ms): ", sw.peek.total!"msecs"
             ,"\nTim(us): ", sw.peek.total!"usecs"
            );
}

void main(){
     auto sw = StopWatch(AutoStart.no);
     string s, str = "4A0B1de!2C9~6";
     int j;

     sw.start();
     for(j=0;j<1_000_000;++j){
         s="";
         foreach(i;str){
             (i >= '0' && i <= '9') ? s~=i : null;
         }
     }
     sw.stop();
     printStrTim(s,sw);

     s = "";
     sw.reset();
     sw.start();
     for(j=0;j<1_000_000;++j){
         s="";
     	s = str.filter!(ch => ch.isDigit).to!string;
     }
     sw.stop();
     printStrTim(s,sw);
}

Prints:

str: 401296
Tim(ms): 306
Tim(us): 306653

str: 401296
Tim(ms): 1112
Tim(us): 1112648

-------------------------------

Unless I did something wrong (If anything please tell). By the 
way on DMD was worse, it was like 5x slower in your version.

Matheus.