This is another version of the Useless use of hash element in void context warning that you might get if you follow my suggestion and turn on warnings in Perl.

This example:

examples/set_default.pl



use strict; #use warnings; my $default_code = 42; my $code = get_code() or $default_code; # Using the code ... sub get_code { # returning some code which in rare ocassions might be undef }

was taken from the article where you can see how adding use warnings to some code can uncover bugs. For example if we run the above code we see no output at all, but if we enable use warnings or run the code using the -w flag of Perl then we get the following:

perl -w examples/set_default.pl Useless use of private variable in void context at ...

As with the other example, here too we can use B::Deparse to uncover the truth:

perl -MO=Deparse,-p examples/set_default.pl use strict; (my $default_code = 42); ((my $code = get_code()) or $default_code); sub get_code { }

The precedence of = is higher than that of or and so the or $default_code has no impact on anything.

This or That

An even simpler case of the problem can be seen here:

examples/this_or_that.pl



use strict; use warnings; my $x = 1; my $y = 2; my $r = $x or $y;

Solution

The solution is to use || or // instead of or and to always use warnings!