Possibly because the ($a,$b) = ($b,$a) requires that $a and $b get pushed onto the stack, and then do a list assignment.

However, in Perl 5.6 on my machine here, I get these results: 
jeffp@hut [3:04pm] ~ #103> perl -MBenchmark
timethese(1_000_000, {
  'swap' => q{ ($a,$b) = ($b,$a) },
  'three' => q{ { my $c = $a; $a = $b; $b = $c } },
});
Benchmark: timing 1000000 iterations of swap, three...
      swap: 17 wallclock secs ( 5.04 usr +  0.00 sys =  5.04 CPU) @ 19
+8449.61/s (n=1000000)
     three: 29 wallclock secs ( 5.96 usr +  0.01 sys =  5.97 CPU) @ 16
+7539.27/s (n=1000000)

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$_="goto+F.print+chop;\n=yhpaj";F1:eval

In reply to Re: simple swap... by japhy
in thread simple swap... by eduardo

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