in reply to Re^3: In-place sort with order assignment
in thread In-place sort with order assignment

@k = sort @k gets optimized by the interpreter into an inplace operation.

When did that make it into the release? Cos everytime it comes up here, I try it out and it doesn't seem to work. (And my attempt to search for the release info fail.)

For now, Sort::Key::_sort_inplace() will do me fine.

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Re^5: In-place sort with order assignment
by salva (Canon) on Sep 20, 2010 at 07:23 UTC
    That optimization was introduced here in 2004. Probably, the first stable release to incorporate it was perl 5.10.

    update: the optimization is documented in perl5100delta.

[reply]

      Hm. Do you see anything wrong with this usage that would prevent the in-place optimisation from kicking in? 

      perl -E"my @a; $a[$_]=rand for 1..1e6; <>; @a = sort @a; <>"

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      Because after the array is populated, memory usage stands at 42mb. After the sort, it jumped to 150MB.

      Which admittedly is substantially better than: 

      perl -E"my @a; $a[$_]=rand for 1..1e6; <>; my @b = sort @a; <>"

      [download]

      Where it leaps from 42MB to 280MB. But it doesn't meet my idea of 'in-place'.

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        Do you see anything wrong with this usage that would prevent the in-place optimisation from kicking in?

        Yes, you are allocating the values in @a as numbers, but as you compare then as strings they are converted to strings inside the sort and perl caches the string representation.

        A little program to show the effect: 

        use Devel::Peek;

my @a = (1.1, 2.2);
print STDERR "allocated as:\n";
Dump \@a;

@a = sort { $a <=> $b } @a;
print STDERR "\nsorted as numbers:\n";
Dump \@a;

@a = sort @a;
print STDERR "\nsorted as strings:\n";
Dump \@a;

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        Under my particular OS/perl combination, stringifying a floating point number, increases its memory usage from 32 to 96 bytes.

        A simple (an slow) workaround is to use two auxiliary variables for the comparison: 

        @a = sort { my ($b, $c) = ($a, $b); $b cmp $c } @a

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