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Re^3: About List::Util's pure Perl shuffle()

by blazar (Canon)
on Jul 12, 2007 at 09:58 UTC ( #626185=note: print w/ replies, xml ) Need Help??

in reply to Re^2: About List::Util's pure Perl shuffle()
in thread About List::Util's pure Perl shuffle()

Update: runrig pointed out that my shuffle was broken. I changed $a[$n] to $x=$a[$n] to fix it. It slowed down my solution, but not by much.

Ok, that's the same trick as BrowserUk's, except that in that form it's even more elegant. Anyway... c'mon! I'm not ashamed the very least to ask why does it work. I can't understand...

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Re^4: About List::Util's pure Perl shuffle()
by ikegami (Pope) on Jul 12, 2007 at 13:29 UTC

    It's similar to print($i, $i++, $i);, at least in effect. Perl must place some form of pointer* to $a[$n]'s value on a stack instead of making a new scalar to save speed and memory. The result is that when $a[$n] is changed by the third expression in the list slice, it also changes the value of the second expression.

    By explicitly copying the value of $a[$n] into another variable ($x), changes in $a[$n] no longer affect the result of the slice.

    * — An alias? A pointer to the SV?

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