I just learned, the hard way, that || doesn't do what I mean in list context. I'm sure it's in the documentation that I read years ago. But I've forgotten.

I commonly use $scalar || $other_scalar. Nearly as common is scalar_func() || other_scalar_func(). What I just tried, and was surprised that it didn't work, was list_func() || other_list_func().

What I meant was "if list_func() returns an empty list, call other_list_func() and use its list, otherwise use list_func's list return." What perl thought I meant was something completely different. 

#! perl -l

use strict;
use warnings;

sub list0 {
    qw()
}

sub list1 {
    qw(foo bar);
}

sub list2 {
    qw(baz zap)
}

sub do_it
{
    list1() || list2();
}

sub do_it_right
{
    my @x = list1();
    @x = list2() unless @x;
    @x;
}

sub do_it2
{
    list0() || list2();
}

print join ':', do_it();
print join ':', do_it_right();

print join ':', do_it2();

[download]
Output: 
bar
foo:bar
baz:zap

[download]
My original code was much more complex - and I'm not even sure how, when it was like do_it, it actually came back with "1" instead of "bar". But it did.

Remember, folks: || gives you a scalar context on the left side of the operator. Just like it says in perlop under "C-style Logical Or". <sigh>

I wonder if perl6 will gives us a bit more syntactical sugar for this ;-)

PS: for those who haven't seen this English idiom, the title doesn't mean || has a bug. It means that I've grown addicted to using it. Sort of like "bitten by the gambling bug" means that one is gambling a lot.

In reply to Bitten by the || bug by Tanktalus

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