"rand @_ is like rand 15, which returns an integer between 0 and 14."

Actually, that's incorrect (with respect to rand returning an integer). The first sentence of the rand documentation reads:

"Returns a random fractional number greater than or equal to 0 and less than the value of EXPR."

As an example (which I'll continue to use below):

$ perl -le '$x = rand 2; print $x'
0.0874574767967786
[download]

I believe, although I can't find any documentation to back it up, that Perl knows the index must be an integer and applies a behind-the-scenes int (or equivalent) to the index. I can use the above rand result directly without getting a warning:

$ perl -wle '@y = qw{a b c}; print $y[0.0874574767967786]'
a
[download]

Even B::Deparse only reports 0 as the index:

$ perl -MO=Deparse -e '@y = qw{a b c}; print $y[0.0874574767967786]'
@y = ('a', 'b', 'c');
print $y[0];
-e syntax OK
[download]

I'd be interested if anyone has more information about this (including, but not limited to, if this behaviour is documented).

Implicit int-ing also works at run-time:

c:\@Work\Perl\monks>perl -wMstrict -le
"my @ra = qw(e h l o);
 my ($i, $j, $k, $l) = (0.99876, 1.00123, 2.499999, 3.5);
 print $ra[$j], $ra[$i], $ra[$k], $ra[$k], $ra[$l];
"
hello

c:\@Work\Perl\monks>perl -wMstrict -MO=Deparse,-p -le
"my @ra = qw(e h l o);
 my ($i, $j, $k, $l) = (0.99876, 1.00123, 2.499999, 3.5);
 print $ra[$j], $ra[$i], $ra[$k], $ra[$k], $ra[$l];
"
BEGIN { $^W = 1; }
BEGIN { $/ = "\n"; $\ = "\n"; }
use strict 'refs';
(my(@ra) = ('e', 'h', 'l', 'o'));
(my($i, $j, $k, $l) = (0.99876, 1.00123, 2.499999, 3.5));
print($ra[$j], $ra[$i], $ra[$k], $ra[$k], $ra[$l]);
-e syntax OK
[download]

Dunno about the documentation.

---

Give a man a fish:  <%-{-{-{-<

++ Thanks for the runtime examples, AnomalousMonk.

"Dunno about the documentation."

After much delving in that musty library beneath the lower catacombs, I believe I may have found an ancient scroll of particular relevance:

$ perldoc perlglossary
...
    dwimmer
        DWIM is an acronym for “Do What I Mean”, the principle that something
        should just do what you want it to do without an undue amount of fuss.
        A bit of code that does “dwimming” is a “dwimmer”. Dwimming can
        require a great deal of behind-the-scenes magic, which (if it doesn’t
        stay properly behind the scenes) is called a dweomer instead.
...

Perhaps, to avoid this dwimmer becoming a dweomer, we should stop poking it. :-)

— Ken