How to test if defined and return value or some default value

Question

In my code, I often write things like this:

my $a = defined $scalar ? $scalar : $default_value;

or

my $b = exists $hash{$_} ? $hash{$_} : $default_value;

Sometimes the hash is quite deep and the code is not very readable. Is there a more concise way to do the above assignments?

Answer 1

Assuming you're using Perl 5.10 and above, you can use the // operator.

my $a = defined $x ? $x : $default;  # clunky way
my $a = $x // $default;              # nice way

Similarly you can do

my $b = defined $hash{$_} ? $hash{$_} : $default;  # clunky
my $b = $hash{$_} // $default;                     # nice

Note that in my example above I'm checking defined $hash{$_}, not exists $hash{$_} like you had. There's no shorthand for existence like there is for definedness.

Finally, you have the //= operator, so you can do;

$a = $x unless defined $a;  # clunky
$a //= $x;                  # nice

This is analogous to the ||= which does the same for truth:

$a = $x unless $x;  # Checks for truth, not definedness.
$a ||= $x;