Hi,
I've just been bitten by this annoying behaviour (using perls 5.30.0, 5.36.0, and probably others): 
>perl -MMath::BigInt -wle "$bi = Math::BigInt->new(10); $x = $bi; $y =
+ $bi; $x->binc(); print $x; print $y; print $bi;"
11
11
11

[download]
As you can see, in incrementing $x, both $y and $bi have also been incremented.
This behaviour can be avoided if I use the overloaded ++ operator instead of the binc() method call: 
>perl -MMath::BigInt -wle "$bi = Math::BigInt->new(10); $x = $bi; $y =
+ $bi; $x++; print $x; print $y; print $bi;"
11
10
10

[download]
Of course, if I want to call a method for which there is no overloaded operation, then I have to workaround it some other way. It's probably not such a big deal, but there's no warning about the danger, and it can lead to some unexpected and puzzling results if you absent-mindedly fall into the trap.

I think I've struck it before ... something to do with the wonderful Copy-On-Write, IIRC.
Is there some way (apart from building perl without COW) to guard against getting bitten by this ?
Is it a bug in perl ?
Is it a bug in Math::BigInt ?
Whatever it is, it certainly doesn't DWIM.

Maybe it's just that this machine is one o' them quantum computers ;-)

Cheers,
Rob

In reply to Action at a distance by syphilis

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