final class random generators?

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2011-09-02T02:30:49Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=6593

CC List

• greensunny12
• Jesse.K.Phillips+D

Description

This is a _potential_ enhancement request.


A wrong D2 program:


import std.stdio, std.random;
void foo(RND)(RND rnd) {
    foreach (i; 0 .. 5)
        write(uniform(0, 10, rnd), " ");
    writeln();
}
void main() {
    auto rnd = Xorshift(1);
    foo(rnd);
    foo(rnd);
}


DMD 2.054 output:
3 1 2 7 5 
3 1 2 7 5 


The mistake is a missing ref, that causes foo to not return an updated random generator, so it always generate the same random values:
void foo(RND)(ref RND rnd) {


To avoid this bug (that I think is common enough), I suggest to experiment if it's performance-wide possibile to turn all random generators into reference things, that is final class instances, that don't require that "ref".

[dlangBugzillaToGithub]

bearophile_hugs commented on 2011-12-05T04:09:43Z

See also issue 7067

[dlangBugzillaToGithub]

greensunny12 commented on 2017-07-11T18:36:29Z

Joe has done an excellent talk about this problem on DConf15: http://dconf.org/2015/talks/wakeling.html