Usually I tend to back out when my own knowledge seems to differ when the majority, but just for the record, my understanding agrees with this guy's guru's. These two while loops are not equivalent (and not for the reasons you think):

# within
while (my $x = $count) {
    $count++;
    last if $count >= 5000000;
}

# without
my $x;
while ($x = $count) {
    $count++;
    last if $count >= 5000000;
}

Benchmark: timing 10 iterations of within, without...
    within: 40 wallclock secs (39.78 usr +  0.04 sys = 39.82 CPU) @  0
+.25/s (n=10)
   without: 35 wallclock secs (35.09 usr +  0.00 sys = 35.09 CPU) @  0
+.28/s (n=10)
[download]

Now, I'm no expert on Perl internals, but it certainly seems like $x is being re-allocated for every loop. At a minimum, $x falls out of scope when the loop ends, which leads me to believe it's falling out of scope for each iteration and being re-allocated. Note that it isn't being redeclared, just reallocated. I'd be interested if anyone has any other explanation...

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