UPDATE: I agree with the reply below that rand does not return an integer.

"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
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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).

— Ken

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!

Thanks!

This

sub rand_elt { $_[rand @_] }
[download]

is a terse version of that:

sub rand_elt {
    my @keys = @_;
    my $num_keys = scalar @keys;
    my $random_index = int( rand($num_keys) );
    return $keys[$random_index];
}
[download]

In my experience, writing a nifty condensed sub like the one below "This" will gain you the questionable reputation of writing "write-only code" at your company or elsewhere, among those which aren't familiar neither with the concepts of perl nor with the language in general. Best is to endure such as camels do - with some sort of सच्चिदानन्द at the beast level for starters, or higher.

Your explanation is perfect—aces—but I assert that $array[rand@array] is a perfectly cromulent Perl idiom and if we are writing our Perl code for Pythonistas, PHPeepers, Javatards, and Ruby fanbois… That sucks the love of being JAPH right out.

Assertion approved. I've been working at a shop where coding standard demanded me to write perl like shell, and worse. No (key => $value) x !! $flag in hash constructors, no statement modifiers, no nested expressions like $array[rand@array] and else. Never, ever, unless. Yuck.

perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'