By doing 
my ($b, $a) = ($a, $b)

[download]
you are not swaping, you simply defined another set of variables. Try this, it will clearly show you what happend, and why it is way fast: 
$a = 100;
$b = 200;
my ($a, $b) = ($b, $a);
print $a, "\n"; #200
print $b, "\n"; #100
print $main::a, "\n";#100
print $main::b, "\n";#200

[download]
Update:

When you do: 
($b, $a) = ($a, $b)

[download]
You are not working against two scalars, in stead you are working against two arrays, and two scalars. Not that it is slow, I don't even think it take less memory as you thought. Although you are not using any temps, Perl is using.

In reply to Re: swapping vars, two ways, 2 results... by pg
in thread swapping vars, two ways, 2 results... by Sihal

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.