duration ctor or addition with duration sensitive to rat/num rand (?)

[robertlemmen]

don't quite understand what is going on, but:

srand(42);

my $time = DateTime.new(1534447684).utc + Duration.new(0.002);
for ^100 -> $i {
    $time = $time + Duration.new(2.rand);
    say "$i $time";
}

gives me:

0 2018-08-16T19:28:04.551037Z
1 2018-08-16T19:28:05.684497Z
2 2018-08-16T19:28:07.604283Z
3 2018-08-16T19:28:07.911050Z
4 2018-08-16T19:28:09.078071Z
5 2018-08-16T19:28:09.513809Z
Type check failed in assignment to $!tai; expected Rat but got Num (1534447727.7935638e0)
  in block <unit> at ./golf line 7

my perl is 2018.04.1-33-ga957b712c built on MoarVM version 2018.04-39-gc702f4c66

[MasterDuke17]

committable results: https://gist.github.com/Whateverable/28d5489d61b59f9c7eca0523da462c13

[zoffixznet]

Golfs to:

dd DateTime.new(<14324937243230497380352387879/9335565490898839500>) + Duration.new(<1043/815>)

Addition of two Rats degrades (by design) to a Num if the resultant denominator would be over 64 bits (after reduction):

    dd <14324937243230497380352387879/9335565490898839500> + <1043/815>;
    # 1534447727.7935638e0

And what's happening here is the addition actually produces such a Rat, and we end up with an attempt to assign a Num into a Rat attribute (the $.tai).

One possible fix would be to use Rat.new with the summed up numerators denominators, because Rat.new allows "overloaded" denominators that are larger than 64 bits and it won't degrade to a Num. However, we still end up with .tai that contains a Rat that'd degrade to a Num in math operators, so perhaps that's a bad idea.

my $a := <14324937243230497380352387879/9335565490898839500>;
my $b := <1043/815>;
dd Rat.new: $a.numerator + $b.numerator, $a.denominator + $b.denominator;
# <14324937243230497380352388922/9335565490898840315>

The other fix would be to have all the .tai operations coerce to a .Rat, so we force the Num back to a Rat, but that's losing some precision due to this roundtrip.

Haven't thought about this much, so there might be much better solutions available.